It doesn't have to be super-high-temp wok cooking. Just using a wok and a normal residential gas stove is not great for you. Even at home stove temps stir frying can throw up a fair amount of oil aerosols. And it potentially means standing over the stove with the gas going on high, even if it's not going to get as hot as a restaurant wok. The gas is bad for you, the aerosols are probably bad for you. It's plausible Asian-Americans use this sort of cooking method more often than non-Asians.