Presumably it’s this study: https://www.researchgate.net/profile/Elissa_Cameron/publicat...

It cited 60% male to female billionaire ratio on n of 350.

But, the methodology was to use google and Wikipedia for research so a more honest claim might be “male offspring of billionaires show up in search results more often.”

I suppose that factoid wouldn’t have been paid for by the publisher though.

Thinking more about my own comment, perhaps researchers expecting to find more male offspring while googling find male offspring more often!

Worth bearing in mind that the birth ratio is generally tilted towards boys, about 52.5%