[intuitionist]

Sub-Saharan Africans are extremely genetically diverse but a sample of ~100 Black Americans is unlikely to have any Khoekhoe or Twa representation.

Anyway it’s possible that the model can pick up on other cues as well; if you had some X-rays from a hospital in Portland, Oregon and some from a hospital in Montgomery, Alabama and some quirk of the machine in Montgomery left artifacts that a model could pick up on, the presence of those artifacts would be quite correlated with race.