How can he sincerely apologize for something he himself doesn't remember and apparently the other party couldn't explain well themselves? If I remembered being an asshole to somebody I'd feel bad and apologize profusely because I am a nonconfrontational person that is terrified of the thought of someone thinking badly of me, but if I learned of an event that is simply described as offensive which I don't remember, I too would just say something shallow like "I'm sorry if I offended you somehow".