I believe Tech billionaires invests in bitcoin. As a head of a tech corporation, they difinitely know about bitcoin and blockchain technology. because it's their work to know about new innovations of the tech market. However, I don't think other billionaires even know about it. Because a billionaire person has a very little private time for their interests. They usually are very busy in their daily routine and business, thinking and investing in bitcoin may not be their cup of tea.
However, it's just my personal thought. I won't be surprised if the fact is exactly opposite.