The case is not "strong" at all. He doesn't even state he supports HBD, only that he thinks some claims made by its proponents are likely enough to be correct or at least hard to prove not-correct. It's a rather uninteresting observation (everyone knows about some of these issues, they just disagree about the HBDers' causal analysis!) that only gets the attention it does because of how understandably contentious HBD is as a whole. The author does realize this of course, that's why he asks that the exchange not be publicized.