That is certainly possible. I think it is unlikely that the metropolitan would not know such things, but it could be that the person I talked to simply did not know and lacked the time or motivation to investigate further.
I would be inclined to think that, because his bishop seemed to know exactly who he was and he seemed to know a lot about him. Also, Br. Nathanael referred me to the bishop. In regards to br. nathanael's perceived "oddness," that seems easily explained, given his apparent background. So, I wouldn't see any reason to doubt the bishop. And, seeing how many people are so offended by br. nathanael, I wouldn't be surprised if some folks weren't anxious to associate themselves with him.
Also, I've noticed how some people successfully market themselves, by appearing "different" from everyone else. He's certainly distinguished himself, in that regard. So, that might have something to do with his success. I don't see anything particularly wrong with it, provided it is restricted to certain venues (like not for a sunday morning sermon).
Also, people like jeff rense (for example), seem to use oddness as a shield. It's hard to imagine anybody treating jeff rense as badly as ernst zundel or bishop williamson were treated, precisely because he portrays himself as a nut!

I can't really fault a guy for that.
Still, with your background, I can see how you might be inclined to think br. nathanael is a fake and perhaps even has a malicious agenda.