Super funny connotation joke, why didn't anyone find Mulan is a woman?

I watched the TV series Mulan Joining the Army and said indignantly to the person in charge of the office, "This historical event is so fake that even a fool can see that Mulan is a woman. But none of the officers who ate and slept with her knew. How is this possible? " The director gave me a look and said slowly, "If you were that officer, would you realize it?" "Of course!" I said, "A woman who lives nearby can detect it with her sixth sense." "You find a female soldier to get along with you day and night, will you be silent?"