I did not know there was ever a link with breastfeeding but I did find this info which now states:
“ As for breastfeeding, there was a time when researchers believed it was linked to osteoporosis later in life. But according to recent research, that’s no longer the case. “After reviewing a large number of studies, researchers now believe that breastfeeding may actually cause positive changes to bone density over a lifetime,” says Dr. Starr.”https://www.hss.edu/article_pregnancy-bone-density.asp#:~:text=“After%20reviewing%20a%20large%20number,a%20lifetime%2C”%20says%20Dr.

I agree with the opinion that genetics plays a large role.