Either he knows, too well, the meaning of "a good person" or does not know at all.
He doesn't want to be labelled.
I'd think that he didn't think he was worthy of such an observation.
I'd also disagree, but I wouldn't beat them over the head about it. They obviously feel that way for their own reasons.
Only that person knows what's really going on in his own head. Maybe he's caring for other people on the outside but in his mind he's saying stuff like 'this person is such an idiot. I don't want to care for this moron, I want to be out getting drunk'
because he is thinking that he is not a good person oc.