China has around 70% [1] of the Bitcoin mining power, and the top three miners hold around 50%, which is so massive, it makes everyone else seem negligible, like an experimental error.
China has the advantage of cheap power, so where you pay $0.14kW/h they pay a fraction of that amount. You can mine crypto, but don't expect it to become profitable unless you have access to cheap power and are ready to break through some of the hardware costs......
Or if you have free student trials for things like AWS/AZURE and can just spin up an instance and run till the trail dies.
Or if you have nationalized power like Venezuela does.
Cheap electricity + ASIC Miners means chinese companies outcompete just about everyone else. Mining becomes unprofitable. Some alt coins manage to sidestep this by ensuring an ASIC for them would be an ASIC for general computing, therefore a CPU.
I think he is referring to the mining operations themselves mainly being in China. Not that the majority of bitcoin is owned by chinese individuals. At least, not yet.
[1]: https://www.buybitcoinworldwide.com/mining/china/