It is just a conspiracy theory so you need to you understand the reality that Bitcoin is not controlled by anyone at least with the current value 51 percentage of attack is not possible and the blockchain network of Bitcoin.
yeah, bitcoin is not controlled by anyone compared with altcoins. The opinion that China has a lot of miners/farm and can make a 51 percent attack is wrong. I assume that it is a conspiracy theory for making more hype only to show that bitcoin is not a good asset for buying or investment.