There's no concept of humanity on the atomic level. It literally doesn't exist. One configuration or mishmash of atoms we call rocks are no different then the mishmash we call humans. Try, without using any high level concepts or groupings, to define what configuration of atoms signifies a rock and what configuration signifies a human.
If you go low enough on any topic the boundaries between categories become vague and the definitions become extremely complex. It's very hard to define what a human is in terms of atoms. The same goes for race, it's very hard to define, at the genetic level what is chinese, and what is not, but the category and boundary exists at all levels, and we can't ignore it.
I've heard of your argument before. They say that the delta in genetic differences between two people of different races is the same as the delta of two people, of the same race, therefore race doesn't exist. This argument is flawed. I believe the "genetic" definition of race is immensely more complex than simply the delta of genetic differences. Here's a more accurate definition: People of the same race have a higher probability of sharing certain genetic traits.
So let me redefine my argument in way you can understand. The people who we label as "chinese" who share similar physical/genetic traits, I believe will be more likely to also share a behavioral genetic trait that makes them more likely to cheat.