I was a bit confused too! But then I noticed the subtitle of the article: "The model of aggression and dominance has infected human society. But new research shows how wrong we got it." After reading it I have figured out the answers to your questions.

> Does anyone have any idea what they mean when they say it's a myth?

They mean that men shouldn't strive to be assertive and dominant.

> What is the myth? In what way is the idea incorrect?

The myth is that you can read news without getting constantly bombarded by inane agendaposting.