Hmm... Almost all of his rep comes from answers to bounty questions, very short answers, many of which didn't collect a lot of up-votes otherwise. Also, although the bounties were offered by different users, a lot of those users appear to share the same Gravatar (== same email address) and appear to have abandoned the site immediately after accepting his answer.
So yeah, a bit suspicious.
This is a bit irresponsible, but I'm going to suggest that perhaps the most reasonable explanation for this is that he is some sort of space alien, come to this planet for the express purpose of taking over the bodies of low-ranking SO users and forcing them to offer bounties and accept his answers. FWIW, this is exactly why the whole "bounty" system has always made me a bit uncomfortable: it exposes SO users to just this sort of space-alien-body-snatcher abuse. As we all know, SO reputation is irresistible to space aliens. They crave it, and will do almost anything to reach 3K (after which they tend to lose motivation rather quickly).