> (Similarly, I would not be surprised if a face recognition NN worked better on Europeans rather than Chinese, for the prima facie reason that they have more variable facial features and other aspects like multiple hair colors other than black.)

You might be surprised to learn that to Chinese people, westerners all look more or less the same. To Africans, white people look more or less the same. Our biological hardware is great at distinguishing minute differences in things (especially people) we are very familiar with, while we automatically start generalizing about things we are less familiar with.

For comparison: a metal fan may be able to distinguish a dozen distinctly different styles of Norwegian Black Metal, while to outsiders it's all loud white noise made by people dressed like undead clowns.