Kindergarten doesn't really matter all THAT much, but by second grade it sure does, especially in private school, which I bet his kids go to !
I suspect his kids go to a private school, too.
I understand what you’re saying regarding Kindergarten as long as the kids know their ABC’s, numbers, etc. However, I think it’s important for them for socializing. Even if someone home schools, as I understand it they have co-ops so they can do and learn some socializing.