I kept asking this b/c I mis-read your initial post. I just went back and now am assuming you were put an an already-scheduled, later flight. Initially, I would have thought they pushed you down to Y if they didn't have any F inventory left. Your follow-up message suggests that they were able to get you up into F, though, making me wonder all the more why they didn't just automatically move you into F to begin with, assuming there was even a single seat open.

Not critiquing anyone here, just sort of wondering out loud. This is the kind of thing that I'm always trying to get a handle on given that I try to fly F as much as possible and therefore always either use miles (for A), stickers (for X) or Y/KUPs (remind me everyone...P, right?). Whenever I wind up in some kind of irregular ops, I always start trying to wrack my brain to remember which policies and rules apply to which situation I'm in...