The sickle cell stuff is likely related to the fact that most "black" people in the US are descended from slaves that pretty much all came from the same small region in West Africa.

The construction of race at any given time and place will tend to have non-zero correlation with genetic frequencies, in part by chance and in part because it is usually largely (but not entirely) drivn by appearance which is to some degree associated with some aspects of underlying genetics.

> e.g. black people are much more likely to have the genetic disease sickle cell anemia.

People with ancestry in sub-Saharan Africa (and within that, even more West Africa), India, the Middle East, and Mediterranean are more likely to have the gene that provides malaria resistance with one copy and sickle cell disease with two than other populations.

While the highest incidence group is also commonly “Black” in most constructions of race, a lot of the American perception of it as a nearly exclusively Black disease is because the population perceived as Black in the US is heavily drawn from West Africa, and the US population also underrepresents other populations in which it is more common than average AND does not include, and may not construct as Black, populations constructed as Black elsewhere in the world where it is not common.