The behavior being described is not what I'd call gullible, but I agree with you that it is unfair to stereotype women with the characteristic.

Was he talking about all women, or just the median woman?

This line of thinking could be used to justify all sorts of stereotypes. Not saying that's good or bad,but one could talk about the median woman, black, white, asian...etc.

Generalization is important. It helps us manage complexity.

When making generalizations, or stereotyping, it is definitely a good thing to talk about the median person.

For instance, Bernie Sanders gets a lot of his appeal by appealing to the generalized, stereotyped american public. Its an incredibly important skill to be able to make those generalizations in order to get appeal. When talking about "Wall Street" his message is not "this is a multifaceted topic". Instead Wall Street is stereotyped to simplify his arguments.