Scratch my earlier comment. As found in the article:

" The scientific literature has provided clear evidence that the ORE [other race effect] and the popular belief that OR faces all look alike are not accounted for by the paucity of anthropometric variations in OR [other race] faces, but by a genuine lack of expertise. Although this theoretical explanation has been supported by numerous behavioral (for a review, see ref. 2), computational (e.g., refs. 3–5) and neuroimaging (6–15) studies on the ORE... "

so yes, it is because we are used to seeing faces from our own race. And no, the researchers are not implying this is a genetic phenomenon.