>How did people even come to this bizarre conclusion?

The first reason is that it is true. All of the best evidence suggests a minor male advantage on g and a major advantage in more specific abilities, such as mental rotation. See https://emilkirkegaard.dk/en/2021/04/the-claim-of-substantia...

It is easy to see why that would be the case from an evolutionary point of view. Ironically, your own post contains a clue: in a male-dominated society where men are far more valued for their intelligence than women, such differences are bound to arise.

The egalitarian bad faith interpretation of this claim is that any man is smarter than Marie Curie. What it actually says is that a hypothetical Mario Curie would almost certainly outshine his real-life counterpart.

The other reason is related to sexual selection. Even if a certain man is less intelligent or physically weaker than most women, it may be adaptive for him to pretend otherwise. What beliefs come to dominate in a given population is determined by reproductive success, not directly by their truth value.