Yes, you have a point. But I would argue that while intelligence operations are commonplace practices of states, direct military actions require more thoughts and it is not something Chinese government would carry out without proper justification.

Basically on this matter, the Chinese government has taken a similar approach as the previous US administration, which is to not take actions. On hindsight of course it is easy to say China (Obama) should have done this or that. But it was quite hard to justify actions against NK until pretty recently. And indeed actions were taken in the form of economic sanctions in light of recent events.