Ish. Arguably. But I think it's a reasonable choice--mysteries of that sort are tricky, IMO.I have run a lot of adventures that have mysteries, in the Sherlock Holmes sense. You naturally want the players to figure out the mystery, but the game does not have mechanics that are quite as strong for solving mysteries as it does for stabbing goblins.
This means that a lot of the time I have to decide whether a choice by a player that I did not plan for can still be useful in the investigation. Generally, I lean in the direction of making the players' investigation be on the right track.
For instance, last night in my game, the party decided to look for clues at the site of a street brawl. I had previously thought of a location where they could get useful clues to identify one of the bad actors in the adventure, but it was not at the site of this street brawl. But because they went there, I moved the clue so that their investigation would provide some forward momentum.
Is that a railroad?
On the rare occasion when I've run that sort of scenario, I've tended more toward "what information is available" as prep, and if the PCs go somewhere it's reasonable to find any of that, they do (probably--I suppose they could mishandle things and not get that information, but ... that's their fault, I think).
I also have tended more toward "solving the mystery makes the next thing possible" than "solving the mystery is the whole point."