Musk also met the mother of this child in college, and they were married just a year or two after - so he was young. He was indeed building his empire when this boy was a child, so as you point out, he was very likely not involved in his youngest childrens' lives at all.
Finally, his first wife is a "typical" Canadian liberal woke feminist - so "transitioning" the child most certainly gave her leftist ego a boost, and was likely revenge against her ex-husband.
Odd how these woke parents who push this on their children don’t go under the knife first.
It is they never outgrew pulling their little siblings’ dolls’ heads and arms off and are now doing it to real live humans.