That's not what the memo said. Instead, the memo claimed women were on average more neurotic.
I guess that a good deal of them are measurably more prevalent in one gender/sex or the other.
Damore point is that if you design a highly competitive system so that Quality A is rewarded but Quality B is ignored you are going to have an imbalanced workplace if women on average have slightly more B and less A than the mean and men the reverse.
The only content of the memo are suggestion on how a workplace could be both fair and more naturally 50/50 by gender.
We should design our systems so that the minuscule differences between men and women are not overly amplified and not abused, not just pretend that those differences do not exist.
That's two paragraphs of the memo in the middle and the bit at the end. Most of the memo is setting up a case for fundamental differences in gender, strawman depictions of the "morality of Google," a claim that men have a higher drive for status (which is, fundamentally, the sort of thing that a company would be put immediately in violation of Title VII if it agreed with), and a claim that Google's anti-discriminatory practices are discriminatory.
In practice the entire content of that document sums up to "Since current diversity efforts are not solving the problem it could be time to admit that the current google structure is on average slightly less attractive or rewarding for women (or for individual in a slice of the population that contains slightly more women than men)" together with some suggestions of what those changes could be.