Right, I played both 8-man and 11-man in high school. It wasn't that much different. You still have to block, catch, throw, cover, make tackles.
You're either a football player or you're not and Carter Nelson is not just a football player, but a D1 - Power 4 type of football player. So 8-man vs 11-man argument isn't a thing for him.
I have a hard believing that a football coach (even at the HS level) would understand how to coach an 8-man team, but wouldn't understand 11-man or vice-versa. If that is the case, that person shouldn't be coaching. You see it all the time where a successful 8-man team goes to 11-man the next year and still sees success. It's because they have football players.