It’s not so much unclear as premised on a number of false distinctions that make it unfalsifiable. For example, at what point and under what conditions does a foreign-born child of Polish immigrants that immigrate to the U.S. become white such that they move from one group to the other? How would you correlate however said group membership requirements correspond to test performance? Why does your curiosity about the relevance of Simpson’s paradox disappear when discussing the category of immigrants, a group with more diverse membership than any of your racial categories, and thus more probable to being prone to its effects?