You can legally own bitcoin. You can legally obtain bitcoin in exchange for goods and services. You don't need to buy bitcoin with dollars. That's how money is supposed to work.
You can legally own dollars. You can legally obtain dollars in exchange for goods and services. You don't need to buy dollars with bitcoin. That's how money is supposed to work.
That's not a bad description of China's exchange controls. If you're in China, and you want to sell goods for dollars, that's fine with the PBOC. You can then exchange your dollars for yuan, if you so desire. That's also fine with the PBOC. If you have yuan in China, and you want to buy something from outside China with yuan, you can do that; import duties may apply. The receiving party can then buy things from China in yuan. They may be able to convert yuan to dollars in Hong Kong.
The key point is that this is tied to goods shipments. China encourages exports, and isn't that hostile to imports. Those are OK. Pure money transactions are subject to capital controls. Part of the purpose of this is to favor doing real business in goods over pure financial transactions.