He is saying that a gender gap, by itself, is not evidence of sexism. A gender gap alone doesn't prove sexism. It doesn't mean that there is no sexism. Sexis

He is saying that a gender gap, by itself, is not evidence of sexism. A gender gap alone doesn't prove sexism. It doesn't mean that there is no sexism. Sexism can be shown in other ways. But he is pushing back against a prevalent mindset that society is a priori sexist until we have equal representation everywhere.