Well, the French and Spanish are smaller than the UK. Scandis and Dutch are taller. Somalians and Kenyans are taller than North Africans. Singaporeans are taller than Chinese people.
Diet does have an effect on height? Yes.
But genetics are stronger.
I know everyone on MN has gigantic children, however, my well-nourished and extended BF children are both smaller than me and DH.
I'm 5' 9", DH is 6' 1". So tall-ish.
However I am from a family of fairly small people, as is DH. My Mother is 5' 1", I have two sisters, the tallest is 5' 2". My aunties are 4' 11".
My dad is an only child of 6'. His mother and father were shorter than him.
My husband is the tallest in his family of seven siblings. His father was 5' 6".
So my husband and I were outliers in our pretty small families, and despite good nutrition and extended BFing, it seems that our children are not going to be as tall as us. DS is 16, hit puberty at 11 and is 5' 6", he hasn't grown much for three years. He may get taller than me, I don't think he will though. He is, however, a perfectly built and incredibly strong smallish person, he is wasp-waisted and muscled. My DD is similarly built. Small, slim, strong.
There's no inherent moral superiority in being tall.
It doesn't mean you were better nourished as a child, it doesn't mean your brain is larger.
It just means you are taller.
That's all.