I think they are Americans. It is not like countries are buying children to win at maths competitions as some do with athletes for the Olympics [0]. It is just notable that they are all of Asian descent. It is also notable that they are all male. You are not instantly racist when you realize that a group that represents a country at a competition or the overall starting field of a competition has different characteristics than the general population.

[0]: http://www.telegraph.co.uk/athletics/2016/07/07/seven-kenyan...