I think it was indeed meant as a distraction @Doombreed ... the key was an attempt to throw you off and probably made you go back to another floor to try it on a door that got another key available later on? I can't remember though...
The thing is that you get that particular key from the bookcase puzzle itself @MrDayCee So it's literally right next to the lock xD. Trying it on that lock, which is in the same frame, and on which no other key works is bound to be the first thing to come to someone's mind
I am going to try finishing the game without doing that. Maybe it's not possible to unlock the final door without doing it. That's the only thing I can think of
Hey @doombreed you might want to check out their site, there is a couple of side games to the series.
They are only short but give some more background.