1. Among the top 12 math students there are only 3 that are not Chinese-origin, and they're all chosen for the IMO team, a bit like AA everywhere to stay politically correct, which is fine. -- I heard about this but could not find the list to verify.
2. Two players in IMO team are having F1 visa, that means they're actually Chinese high school students that are studying in USA recently. This is very debatable, many disagree on this practice, and the physics, chemistry Olympiad do not have the same practice because this practice does not represent/honor/encourage the real math talents from US.