No, I don't think he agrees with neo reactionaries any more than he let on. In his public posts he has praised reactionaries for making observations that most shirk away from, even if they are wrong in their conclusions. This is pretty much what is expressed in the contents of those emails.

I think you're reading way too much into one sentence saying human biodiversity is partially correct (which is not actually a particularly contentious idea when you explain what it is), and leaping to the conclusion he agrees with neo reactionary claims that some races have substantially lower IQ even with identical environmental factors. There's a vast disparity between "IQ disparities across races" and "IQ disparities across races, without environmental differences" that is crucial to understand.

unfortunately i don't think neoreactionary views are at all orthogonal to the political discourse that is current in the usa; moldbug has his own variant of the 'cultural marxism' thesis, though naturally enough he doesn't blame it on the jews or the frankfurt school; instead, he picks the quakers, which i mostly agree with (except that of course i agree with the quakers)

his criticism is squarely directed at the mainstream us left that he grew up in and its core ideals, such as equality, human rights, pacifism, fighting injustice, etc. he thinks all those are bad things