It's certainly possible. I do think it's clear that this isn't simply a matter of a hateful individual, he's clearly mentally ill. Although I think hate can be as much a mood disorder as mania or depression or anxiety, just one that it's a lot harder to sympathize with.

It's hard to be sure about something like this, unless somebody actually manages to diagnose him with a b12 deficiency, and supplementing reverses all this stuff. The article mentions a lot of drugs as a teen, that can be a factor, and the timing of these awful behaviours is right in the prime years for psychosis, it's sort of hard to say that his brain wouldn't have gone sproing on the standard diet.