I see the memo personally as more young-and-naive and I'm not one who thinks naivety is something that should get you fired, per se (though, much of his whines at the end were directed directly at Google being explicitly anti-conservative; rightly or wrongly, employees who noisily complain in public about their employer do often get dismissed). But he certainly wade into some touchy waters armed more with opinionated commentary sources versus hard science. There is a century's worth of troubling eugenics-oriented history on that "IQ and biological differences" quote that should inform one that this is not a remark to toss off lightly, and merely semi-support that with a link to a conservative think-tank link (that itself IMHO was pretty naive).
Chop the last bunch of the manifesto and it would be more interesting, but as it stands, the memo was not just "men and women are different" and how that applies to STEM careers. In the end, it was also a whine about how Google is Capital-L Left and "alienating conservatives" too.