Let me say this: I tell my buddy where I'm going, in case he needs to get a hold of me. I let my roommate know when I'm going to be back, and does he need anything while I'm out?...
These are not hard things. Communicating one's direction, departure and arrival is just plain consideration for other people's time.
My first question is this: Why have you not been introduced to this person yet?
As far as your reaction, I'd say it was practical.
Second question: Does he not have his own key?