You seem to say that any time the DM puts an unexpected obstacle in the way that stops them from succeeding, it's railroading.
Can you please quote me saying that? If not, please stop attributing to me views that I don't hold.
Any time a plan by the players works but they didn't get the results they desired
This doesn't make sense - in that, the definition of a plan
working is that it produces the intended/desired results.
What is
railroading is the GM making up stuff, without regard to any action resolution procedure, in order to shape the fiction in the direction they desire without regard to the players' intentions in declaring actions for their PCs. One example would be a GM making up fiction pertaining to an interrogated NPC in order to block the players' intended line of action (ie gathering information so as to take the initiative in a conflict) and force the players back into the passive role of responding to whatever the GM has next on their list of events to describe.
Any time the GM runs an NPC in a way that you don't expect or don't care for, it's railroading.
If this is your take away, perhaps you need to re-read my posts.
If I fail a check, I expect to suffer adverse results in the fiction. If the GM has notes that specify certain facts, and I fail in declared actions to acquire those facts, I expect to proceed in ignorance of those facts.
But if the GM makes up fiction with the sole purpose of rendering a declared action unsuccessful, in a context where I and my fellow players have spent a significant amount of time at the table working up to that action in order to try and exercise some influence over the direction of play, than that is a railroad. Basically the textbook definition.
I mean, suppose that the module had instructions to the GM:
Any time the players try and obtain information from a NPC, make sure they are unable to do so by playing the NPC as cognitively incapable of understanding the PCs' questions and providing answers. Are you really insisting that that would not be instructions to run the game as a railroad?
Please correct me if I'm misunderstanding because it seems like what your real complaint is boils down to default style D&D not being a different game. You seem to want more of a narrative story telling game (or whatever the "proper" terminology is), something more along the lines of a PbtA game. That's perfectly fine. Those games have certain checks and balances D&D doesn't have, and personally I don't care for that structure, but we all have different preferences.
D&D does not have to be a railroad. I have multiple sets of D&D rulebooks - Moldvay Basic, Gygax's AD&D rulebooks, the 4e rulebooks - which set out approaches to D&D that are not railroads.
You seem obsessed by the idea that I should not be playing D&D. But I have been playing D&D (on and off, but with quite a bit of "on") for over 40 years.
I had a DM a while back that basically told us that if we could come up with a convincing narrative, if we could make it sound interesting, that it would work. So we had one player that was wrasslin' huge monsters into submission because she was enthusiastic about it. In another case a player was able to plug a cave hole because the player happened to use a mini for their familiar happened to fit the exact size of the hole in the terrain piece the DM was given. The players were given a lot of narrative control over the game. Given a choice I would never play with that DM again.
What does this have to do with anything?
If you want to know what I think a good non-railroad game looks like, you can read any of my actual play reports. You will see that they in no way resemble what you describe here (which also has absolutely nothing in common with Apocalypse World). You are describing a game of free-form resolution, as best I can tell.
I am simply talking about the GM applying action resolution rules.
There are terrible DMs out there.
But you seem absolutely convinced, for reasons that escape me, that the GM who had five players leave his game was not one of them. I don't know why you feel the need to carry a torch for this guy you've never met and his game that you've never experienced.