No one writes unless he believes that what he writes will be interesting to someone.

Yes they do. People write for the love of writing. There's a long history of writers and other types of artists who hated their own work/did not think their work was very good. And Twilight alone can prove that some people write for themselves and let it find an audience, IMO.

As someone mentioned, he has a certified genius I.Q., and that's hard to hide.

No it isn't. Hell, just down the road is an older man who I kind of wrote off as a slightly wacky neighbor for a long time, until my mother started telling me about all the great things he did before he retired. I talked to him myself and, sure, when he got on a subject he knew about/was passionate about it was obvious he was a very, very smart man, but, you know, he's still also the slightly wacky neighbor.

I think the key is not rubbing it in everyone's faces. Besides the fact that touting a "certified genius IQ" sounds ridiculous to start (it doesn't matter that it is a thing, it still sounds stupid to throw the term around like that), the attitude makes him come off as the opposite part of the Dunning-Kruger effect than the side he claims to be on.