I'll say this of the games pics I've seen and the two I attended this year so far, I'd say Asian dominate the game probably around any where from 40-70% European descendent accounts roughtly the remaining 30-60%. I haven't seen many South American or African background (it would be kinda cool to have more multicultural)
As for sub categorizing...
Chinese, Japanese, (top two) and Thai, Phili basically is all the airsofters, there might be few Koreans, Cambodian, Mongolian, or Vietnamese but largely its the big four
As for European Descendents, for most part they just refer themselves as Canadians, or they're so multiculturalize that I fell asleep as they try to name em all. (And some which I can't tell at all)
Keep in mind this is base from Canada, and I'm generalizing like crazy.