It might not be a single person, but who knows.  I've been fairly confident that whole families engage in bounties, sig campaigns, and whatever else, and there are probably community bounty farms whereby all the members pool their funds together into one wallet.  But in the end, it's impossible to say what's really going on when you find crap like this.  When accounts are tagged, you'll start hearing all sorts of excuses and pleading--but there's just no telling what the truth actually is.

With this many accounts, though, I doubt it's a single individual.  Possible but unlikely.