Sounds like he is resource guarding the area where he is sleeping or wants to sleep…(I have one that does this). I don't know why guarders warn off some people, and allow others to do whatever they want to them. It is a fairly easy fix to train them to get down from a bed or couch before you sit down, or when you want to sit down. Also, for the record, any dog of mine that continues to resource guard in the bed...as in, if someone bumps them, dog or human, they respond with a growl, doesn't get to sleep in the bed anymore. I might excuse it once or twice if they knock it off when directed to...but if they can't keep from doing it, they can sleep in a crate