That’s true — race is a social construct if you define it as a social construct. But it’s rather odd to say that a child of two Kenyan immigrants is of a different race than his parents, or that someone’s race changes when he moves from place to place. “The importance of one’s race,” or even the perception of one’s race (if one is half-African and half-European, is that black, white, or mixed?) might change, but race itself does not.
Merriam-Webster defines race as “a family, tribe, people, or nation belonging to the same stock.” Steve Sailer calls it “an extremely extended family that inbreeds to some degree.” Both of these strike me as much-more-usable definitions, and both are rooted to some degree in genetics, not social constructs.