I think you're approaching this in a smart way, FWIW.
One other thought that comes to me: concern with fitting in often has more to do with personality, I think, than anything else. Extroverts tend to care more about it than introverts, for example. Especially if the introverts have some outlet/s for discussing their interests.
I think I'd talk about it with him in a laidback way, just to be sure he's experimenting. I'd probably discuss the pros and cons of intentionally doing less well on schoolwork. That could come back to bite him if you want to try to advocate with the school at some point, and I really do think that is qualitatively different than being silly with friends on the playground to get along with others, you know?
