The “impurity” of menstrual blood explained by my Quran teacher.

6th grade elementary school, My Quran and Islamic studies teacher gathers all female students of my grade into a classroom because it was about time to “have the talk” with us. She starts explaining how we’re gonna bleed every month and the reason she gave was rather interesting. She says, While we’re still in the womb, we ingest dirty blood from our mothers and it gets lodged in the uterus, which comes out every month as menses. Now we know that’s bullshit because the endometrium proliferates every month and sheds off. Even then, i could still make out the stupidity here because by that logic, men must get periods too. So i asked and she pulled a Zakir Naik on me (said everything else but answer my question)😭. Is there a hadith regarding this or she didn’t have any brain cells