The professional math world is full of smart but delusionally ambitious people who do things like focus all their energy on the Jacobian conjecture and the Riemann hypothesis. Most crash out never finishing their doctorates (because these problems are too hard and working on them does not provide what it takes to survive professionally). Zhang is an example of such a person. What is very unusual about him is not that he continued to work on such things anyway, rather that he eventually found some measure of success. What I infer from his story is that he is tremendously stubborn and genuinely oblivious to ordinary material feedback. Evidently he has some talent too, but that's not the unusual part of his story.

Said another way - I've known quite a few people like him to a point - with the difference that none of the others ever produced good mathematics, much less solved a major problem.