That's not necessarily so; you could require mice to be heavier than 90 grams, and elephants to be heavier than 80 grams, and still have your elephants be heavier on average.
(I don't want to wade into the bigger argument, just pointing out that "that's simply how statistics work" only under certain conditions (which most likely apply here, but you wrote "there's no getting around that" when there is)).
What I inferred from this, is that he learned that at least in some cases, there's aspects to Google's diversity hiring that they'd rather people not know about.
Now I don't know if this is false, true, or true within a small subset of Google; but his claim of the secret meeting does change the narrative somewhat in his favour.
Basically, you're asking for evidence so that he can prove himself plausibly innocent of a crime that there's no evidence for in the first place.
Incidentally, we do not know whether his statement is true, or whether the changes to Google's hiring practices have changed the employees' operational capability.
In the absence of this information, with such a clearly (if somewhat subtly) stated opinion, it's natural that one would be offended by his words.
Before accepting a statement like his, it would behoove us to know what the actual policy changes are.
Yes, but that's simply how statistics work. If you require one group of people to score 90 on some test in order to be hired, and another group to score 80, then among successful applicants the second group will have lower average scores than the first. There's no getting around that.
The argument should be over whether or not Google's hiring practices lower the bar for particular groups of people. If they do, then the above conclusion about the average talent of various groups is inescapable.