Why is this guy nice to me but unfriendly to others?

So there’s this guy in my building and I’ve noticed (I haven’t done anything to earn any kindness from him lol) he will hold doors for me and like do mini favors for me like getting my floor for me in the elevator and I notice he softly smiles when he sees me.
But he was cold to the front desk staff and didn’t smile back at the lady who works at the front desk and looked annoyed at her for not pressing the button for the hall to the elevators to open. And I was talking to the front desk lady and she thought he was rude. I can’t tell if he just doesn’t respect people in certain positions or if it’s personal and he likes me in some way? I don't know.

Why is this guy nice to me but unfriendly to others?
Post Opinion