Everyone has the potential for magic. Magic can occur in a child whose parents are muggles, non-magic people, and whose family has no history of it. Magical people can have children who cannot use magic. It's rare in both cases, but it can happen.

[ This is not really an interesting topic for him, and he doesn't sound very engaged. And he's already bracing himself to totally railroad and potential conversation about blood politics, for the record. ]