As a policy it denies both women and men the opportunity of working together. If you are a man and a woman happens to be working on the same problem that you are investigating, would you like to be excluded from learning from her? And vice versa.

Exactly. So his proposal is not a practical solution to the problem of human behavior affecting productivity, but it’s not “sexist”. Many single-sex schools exist and have strong proponents, but are rarely described as “excluding” people.