NK trains up and operates hacking groups to generate income, not just to be unpleasant. So, guessing that would mean NK is renting out hacking services to China. Other ways to generate income from hacking is operating a ransomware gang, renting out botnets, and gathering banking passwords to use in draining accounts. We may assume they are involved in all of the above.

That's the wrong takeaway from that bit though I think. I believe they are saying that China and other states are the actors on behalf of NK not that they are using NK as patsies ... granted that may also be true. International politics and espionage is a weird domain.

I think the implication is that these are North Korean hackers stationed in China, not that China is doing it on their behalf.