Facebook puzzle?

So around six months ago a close friend and I stopped talking very long story as to why it was hard for us both he  blocked me on fackbook Completley at the time i went on my Facebook messenger the other day and he came up both the accounts he has as he has two it says he is on messenger and will get your message instantly but yet still blocked on facebook itself which baffles me as I thought u had to unblock on facebook first to unblock on messenger.. is it possible to just unblock on messenger and not on facebook or has facebook gone wrong somewhere just find it odd thought he might of wanted to reach out again just don't get why he's popped back up on my messinger ????