Do you think that Diane's advice about how to act like a man was accurate? What about it made sense base on your experience...

According to me, Diane's advice is not relevant. It could be an accurate advice to act like a drag king or like drag queen, in other words to act excessively and then not naturally.
Acting like a man means that all the men behave in the same way and according to Diane, men don't smile. When there's another known generalization which says that "boys don't cry", she says that boys don't smile. So how should a man behave?

Diane mistakes the category "men" for something else, maybe the men called "macho" very arrogant towards women, thinking that men have to control women.

This kind of mentality can be dangerous beacause it closes the people in false identities.