Sex Reversed Cultures A Myth

I'm not sure if I am understanding Steven Pinker (from the video in class) correctly when he said that sex reversed cultures were a myth. I'm interpreting 'sex reversed' as gender traits that vary from our culture's 'typical' understanding of male and female. In a previous class I took, we studied other cultures where each sex took on the opposite gender traits. Females took on the stereotypical male side while males fulfilled the stereotypical female role. The culture I'm going to use as an example is a primitive society known as the Tchambuli. Margaret Mead wrote "Sex and Temperament in Three Primitive Societies" where she discusses how when she and her colleagues studied the Tchambuli society, they "found a genuine reversal of the sex attitudes of our own culture, with the woman the dominant, impersonal, managing partner, and the man the less responsible and the emotionally dependant person." Mead attributes all sex characteristics to being socially conditioned. Also, looking at animals, Bonobos, a primate closely related to humans and chimpanzees, also have a very different approach to gender. With females being in charge and sexually aggressive. Many matriarchial societies seem to exist so I don't know how Pinker can say the idea is a myth. There are also Native American cultures such as the Pokot, Navajo, and Mohave tribes that have very different sexes. How did everybody else interpret what he was saying?