I have only a wild guess. Only the most successful people from another country are offered the opportunity to come here. So the random native Nigerian who has moved to the US is probably a better candidate than your random native American of any race.
As an Immigrant to the US who could not make it big and had to go back(to India). It's not the most successful people, it's the most successful people in the prime of their health, career, academic and family situations. It's like everything that makes one fall in the top most cohort of people in history needs to happen to an individual. It's not just individual ability or hard work or talent. Everything from health and family situations to personal career situations just needs to work.
We are not just talking of the best people of the human race, we are also talking of the most luckiest.
US immigration is a combination of all those great Human enterprise things plus a very brutal lottery system. In short a very powerful filter that just picks the most successful people and makes them succeed further.
That’s well beyond my knowledge of race issues. Maybe others have some data. I’ve seen it at a number of companies. To the point that before a black engineer speaks, Ive got a Bayesian probability precomputed on what accent I’m likely to hear.