I know you didn't imply any of that, most of it was my speculation, the subject interests me. But saying that the source of his problem is his own self-hate, is saying that its all his fault...
I myself am not very social at all, but I don't hate or even dislike people. My reluctance to socialize seems more out of habit to me these days, and I have my various theories as to how it might stem from problems growing up. What social interaction I do have, I get along just fine. And I definitely don't hate myself, maybe there is something wrong with me but it isn't self-hate. Unsociable behavior can be caused by more things then self-contempt. And really I think self hate would cause bitterness and hostility rather than apathy.
And as I was saying one can't really hate "all people", unless one is suffering some kind of severe psychological problem. "All people" is an abstraction, you can't meet or be around all of "humanity". That plus the fact that this sounds like something that has only afflicted him recently, makes me think we can look for the source of the problem in something that happened to him regarding his relationships/interactions. He didn't just start hating himself.