There is a massive difference between there being a biological basis to some of the phenotypes associated with racial categories and there being "biological meaning" to identifying races.

"Black" represents a wide range of genotypes, many which differ more from each other than from "white" individuals and populations, even if there may be other tendencies like bone density and novel genetic features that appear more commonly or exclusively in some subsets of the "black" population. The skin colour phenotype being (usually) darker just happens to be very easy to notice and have acquired a lot of socially constructed meaning. Except in the narrow context of skin tones, it isn't biologically meaningful to consider "black" people as a particular group though, particularly not compared to more specific genetic markers that don't have the same socially constructed meaning...