Just look at the way Julien Wanders is shaped. It's very atypical for a white athlete to be as stick-thin as he is. Many white athletes are thin, but you can see that they are just skinny guys fit onto a mesomorph skeletal structure. Ben True and Andy Vernon have mesomorph-like bodies.
Julien, on the other hand, has incredibly small calves and has East African-like body proportions and limb shape. He has a Nilotic physique - just look at those springy, stick-like limbs that remind you more of Kalenjin than of Swiss people.This is why he is so fast.
There are several papers mentioning how East Africans are so successful not because of their VO2 max, but because of their morphology and excellent biomechanics.
Look at the way he runs. It's incredibly Kenyan-like. Most white runners simply don't run like this.
Incredible.