If you take a closer look at his family ( his father in particular ), you'll see where this kind of behavior comes from.
I mean, his father rather recently married the daughter of his ex wife. Granted, it's not his daughter / her Mom isn't Elon's Mom, but he was a father to her growing up ffs.
In the interview he said, that women are not anymore desirable after a certain age. That's why he opted now for the daughter and wants to make as many kids as possible with her. You know, he really believes his genes are superior and must be spread as wide as possible. Her Mom is living with it, even supporting both.
I paraphrased, but he's really a very special kind of asshole.
I can imagine that it wasn't fun, growing up as musk senior's son.
It's no excuse though.