Maybe he is thinking deeply or worried about something, I tend to ignore everything around me sometimes. Example from what happened few months ago: My perspective, I came home thinking about something, dropped my backpack, washed hands and came to pc to Google and write about it before I lose it in my train of thoughts. My exes perspective, I just passed next to her siting on a couch without saying anything came to pc and started writing. She's thought I was angry so she became angry and ignored me until I made first contact. And I didn't realized what I did until I saw her reaction. It was a laugh when we talked about it, but things like that can happen to people.