What's certain is that I "open"ed the door and it opened before I removed the tile where the blue lock is.
I don't know if the door was always unlocked from the start or not.
I don't know if I owned the blue key or not at that moment.
I don't know if I ever used the blue key or not on the spot (before revealing it), it's possible that I did.
Don't bother with the hook, I mentioned the hook because the bar with the hook is what helps you get the bottle where the hint about the location of the blue lock and I didn't have this hook (nor the hint then) when I opened the door.