Or am I mistaken?

Yes

Yeah, I’ve heard about that, but right now China is second in terms of billionaires after the US.

Yes because China has a very large population and thus all absolute numbers not adjusting for this will be extremely large and out of step with reality. In reality the rate of billionaires in China is 0.288 (Between India and Kazakhstan while being far less poor and far more advanced) where as it is 2.42 in the US and 0.821 in Russia for example.