Diet and hygiene can obviously influence your max height, limit acne, promote brain development at a young age, etc. I have even read twin studies before that talk about how even some aspects of bone mass are environmental. Just because much of our life is genetic doesn’t mean everything is immutable since birth. Luckily, most of us will never reproduce, because if we did, our kids would be at a bigger disadvantage than necessary. “Milk is a cope and too expensive, feed him dollar store root beer instead.”
I’m not saying the diet proposed is correct, just about the concept in general. Northern Koreans used to be taller than Southern Koreans and the Japanese 80 years ago, but they’ve been dwarfed. There was no genetic selection in SK and JP significant enough to only breed taller people, the role reversal is likely environmental.