I'm curious, how does he manage that? I would have expected that an executive position involved a lot of time at work, and that it would be difficult to combine that with being an involved homeschooling parent. Or is there some version of homeschooling where the parents aren't spending much more time with their kids than they would if at school?
Many homeschooling parents find they can accomplish in about four hours what public schools do in a full day. Considering the personal attention, study halls, and such, this makes sense. Next, the parent teaching doesn't need to try to figure out where their student stands with quizzes, tests, and assignments because they manage it already. There's generally one parent at home doing all this, but the time needed is much less than it sounds initially.
So much time in school is indeed wasted. I'm pretty sure the amount of actual material I covered in high school I could have done in 2 years, easily. I was snoozing at that pace.
It also depends on your child. If your child is more of an independent learner, or one who pick up material fast, it would be much easier.