This is interesting timing given what has been happening related to Evergrande. It is possible that the government is worried about money being moved out of the country, and cryptocurrency is one way of doing that.
1. Find a place that takes RMB and gives you crypto.
2. Send crypto to your wallet or foreign exchange.
3. Abroad, sell crypto for non-RMB fiat currency.
No mining needed.
China can't ban 2 (or perhaps they could by putting the great firewall into overdrive) so they are banning 1.