The memo literally lists the biological/psychological traits of men and women that may have caused the gender gap in tech. (He tries to clarify that he is talking on a population level and not talking about individuals)
In other words, he was saying there is something in tech culture which is inherently less palatable for the average woman than the average man. He never claimed that the culture was good and the women were deficient. Instead he said the culture should change instead of artificially trying to fill it with equal ratio hires.