As I posted upthread, this seems like "living sandbox" play.
My impression is that it is you, the GM, who are introducing the cultists and their amassing of weapons and the hellcats and their stalking of the PCs into play. Is that correct?
I mean...yes? But those were both the results of rolls. The former was a (highly elided, the actual scene was much more detailed) 6- on a Discern Realities check, which I run as the party learns a truth they wish wasn't (so there's no lying or distrust, instead a threat often escalates).
Trying for brevity: They had been fighting some evil druids, but felt they'd done enough to deal with that threat and moved on. They went looking for new challenges. After some rolls (Spout Lore, Supply, and Carouse, IIRC, the Supply because someone wanted to buy a magic shield but got a 6-) they heard rumors about weapon caravans disappearing on the trade roads. They decided that this clearly needed investigating, so through merchant contacts of theirs, they set up a meeting with a prominent weapons merchant. She verified the rumors, saying it was bad for her business and jacking up prices, and they asked her if they could help. Together, they hatched a plan to male a fake caravan so they could find and eliminate the raiders. Plan went well, and the raiders (the aforementioned cultists) took the bait. The party secretly tracked them back to a secret, Forty Thieves-style sanctuary hideout. PCs opted to infiltrate, stealth their way through, and ambush the cultists. A pitched battle followed, but the party defeated their opponents and managed to salvage one of their shadowy magic weapons. They then gained much from the hideout's library (another Spout Lore, just driven by the available books rather than personal knowledge, plus Discern Realities), both other locations of interest for the cult, and doctrinal info about why this cult does murders and where they come from (e.g. the already-hinted but previously unexplained connection between this cult and the proper, non-murderous Safiqi priesthood; the cult is a heresy of the Safiqi, not just random murderers). In searching for the things stolen from their fake caravan, the party Wizard got a 6- on Discern Realities, so they learned that there
had been a very large stockpile of weapons here...but it had relatively recently been moved elsewhere (an unwelcome truth). This implied that the cultists had begun mobilizing and were thus a bigger threat than merely disrupting commerce the party had interest in. They then decided that they needed more time to make sure their intel gathered here wouldn't expire too soon: if the cultists knew this info had gotten out, they'd just abandon the identified sites. So they concocted a great deception, making it look like nomads had stumbled onto the place and ransacked it, with the cultists themselves seeming to have destroyed the library to prevent it falling into the wrong hands. Using the Battlemaster's knowledge of Nomad military tactics, the Wizard's fire magic, the Druid's ability to mimic weapon damage via claws, and the Bard's eye for detail and storytelling to catch any loose ends, they collaborated to make the deception near-perfect, meaning the cultists would never suspect a thing and giving the party all the time they could want for investigating the sites they'd found in the records. (Unfortunately there was no legend for the map they found, so they couldn't say for sure what the various sites were, just that they exist and probably serve different functions.)
I planned exactly four things in all of this, one of which had already been strongly hinted, i.e. that the cultists have a historical connection to the Safiqi. The second thing was the existence and overall layout of the hideout (the stolen weapons had to go somewhere after all!), third was a single point of doctrine (the cultists believe they see enlightenment in the moment of another's unexpected death), and fourth was the cultists' statblocks. (I am far too slow at inventing combats "on the spot" so if a fight is even a little likely I try to prep it in advance. That way, my players aren't sitting there, waiting, as the tension bleeds away.) The reason why the cultists are amassing weapons? Where did the weapons go after moving out? No idea! We'll learn all that later, if it remains relevant. I have not planned any of the sites they learned of either, in part because "draw maps, leave blanks," in part because this feels to me like a perfectly valid place for pure improvisation. The party actually has yet to visit more than one or two of them, IIRC, as they've had other priorities in the meantime. But it's only been a couple months in-game, so it's not too weird that that could happen.
As for the hellcats, that happened literally last session, and was the result of a 7-9 on a Perilous Journey roll. They didn't get the drop on the danger (which I invented very quickly because I had had zero prep time for this session and just used the first monster in the Dungeon World Codex that sounded interesting to me), but the danger didn't get the drop on them either--each saw the other in advance. Thus, the danger was
stalking them, and they had one chance to try to avoid a fight from hungry semi-elemental beasts of shadow and fire. They succeeded with flying colors due to coordination between the Battlemaster and the Bard (who has learned how to take certain animal forms, taught by the Druid); essentially the party feinted and the Bard used shapeshift sexy no jutsu to sic the hellcats onto some male antelope in the area. This gave the cats what they wanted (food) without needing to fight. I'd never considered hellcats as a creature prior to that Perilous Journey; the desert is known to be full of monsters though so one appearing is not unusual in the least, especially if you travel off the well-worn trade routes where the monsters have already been cleared out.
Also...I have to be honest, I feel like I'm being squeezed a bit. If I'm speaking in abstractions or invented examples, well I'm not saying WHY the players are doing some given thing. If I give examples from what I actually do and have done, either there isn't enough detail, or the specific throughline is bogged down by details, could I maybe state a definition or other, you know,
abstraction to make it more clear what I mean? Etc. I don't think anyone is being aggressive or whatever, but like...I feel like when I meet a request I'm always told I've fallen short in some other way that makes it impossible to say.
Also, it's extremely confusing (and somewhat frustrating) to me this notion that having ANYTHING AT ALL pre-planned is almost...infectious? That it basically beats into your players a passivity that
will, always guaranteed definitely, spread to every other action they take until all they do is sit there silently until prompted and otherwise just passively glide from one totally ridigly pre-planned scene to another. That...doesn't match my players' behavior (well, other than one specific guy, but he's very new and is afraid of "playing wrong.") I don't understand why you can't have healthy, vibrant, sustained Story Now right alongside judicious, circumspect use of Story Before. Someone presented it as though Story Before is...like an invasive species, as though it were simply axiomatic that ANY amount of it no matter how small will eventually spread and take over the game and beat the players into passive, meek little followers of the DM's hard-coded narrative.