Well no, East and South Asian immigrants to the United States do tend to outperform the median in their country of origin. Acutely, in the case of South Asians.

So that's half of the statement, the other half is that those two groups are not a large fraction of the total immigrant population. As such, they affect the conclusion, in the sense that removing them from consideration would make the difference in question starker, but they do not change it, because it's a statement about a whole of which they are but a part.