Here is my guess. It is not the jet but the engine. Hence China can approve the planes with their jet engine for commercial use or China use the engine for its own commercial jets.
I believe China cannot buy fighter
jets from the US and they buy them from Russia. On the lighter note, we
can sell China all the missiles and jets with a built-in GPS. When
they're directed to us, they will be automatically returned to senders -
just like Elvis would sing.
On the similar topic. China had a deal with GE for buying their engines with a clause of technology transfer