A plethora of evidence for genetic influence of American race-ethnic gaps in intelligence

I have some questions regarding this research :

First, "race" is a very poorly-defined notion, and has only indirect correlation with haplogroup-based populations. So, two people that describe themselves as "black" can be genetically very different even if they both have African ancestors. Moreover, "black" put in the same category peoples that originates from africa or −e.g.− australia.

My second question is about a factor that I did not see consider in the research (maybe I missed it) : in North America, a big part of the population migrated from Europe, Asia or Africa. Could the causes of these migrations have created a kind of selection bias ? I mean, the peoples that came to America weren't randomly selected... One the one hand, from Africa came mainly slaves, that were captured. During slavery, it can also be hypothesised that people with above-average intelligence were not favored. On the other hand, people that decided to emigrate to America showed a trait (willingness to go to unknown territories) that might be related to general intelligence.

To be honest, the author try to tackle the first question in their research (figure 2), but I have a feeling that using socially-defined groups (race) instead of biological-defined ones may be a hint that the genetic influence is ingrained by social behaviours through selection.