Heartbeat & gender.

So this girl that's pregnant insists that I am having a boy because last checkup my baby heartbeat was 150. She says she's having a girl because her baby heartbeat was 163. I tired explaining to her that my first born heartbeat was 160 & he's A BOY 😂. Why do a lot of women believe that their baby's heartbeat has to do with its gender? It's kind of annoying too, being that I feel like I am having a girl, call my baby girl as well. I called my son a boy, & knew it from the beginning and that's what he turnt out to be. If this wives tale truly true? Or is it bullshit as I believe it to be because my first born was proof 😂.