You can see it in the paper how he starts with the obvious, "Men and Women are biologically different" and then jumps into observable personality differences, which are not proven to be biologically driven. It wouldn't be so bad if he didn't attribute these "biologically-caused" personality differences (neuroticism, agreeableness, less ambition, etc.) to women being the ones to blame for their problems in tech.
This opinion is toxic to his coworkers, which is a violation of the Google Code of Conduct.