Well, basically here (Russia/ex-USSR) you can look at name to understand person’s ethnicity.
If surname is Li/Yan/Ten/Tsoy - that person probably comes from ethnic Chinese or Korean background; Manukyan - Armenian; Rabinovich - Jewish and stuff like that. Of course there is fighters with Russian roots from Brazil, North America, Hong Kong, Australia and other countries or Chechens from US and a dozen of European countries.
Like, when you see surnames like Matsumoto, Choi, Dos Santos, what do you think? I think that person with such surname are probably have Japanese, Korean, Portuguese roots. And in reality they can be from a lot of countries, like there is Brazilian and Swiss fighters with a Japanese surnames, Swedish and Canadian with Korean, American and Swedish with Portuguese. Same here. For example, I remember interview with fighter Sergei Choi - ethnic Korean, born in Tajikistan, lived there, then in Uzbekistan, then returned to Tajikistan, then moved to Russia and currently lives and fights in South Korea.