China has been way less cautious over the past four or five years, and I do not think Trump being in office is a coincidence.
At the same time, Trump is deeply insecure, and is attached to the idea of military power somehow reflecting his own masculinity. Look at his tweets in response to North Korea's provocations, for instance, and how he made them all about him personally. So I think China was careful not to take action that would cause Trump to feel slighted or emasculated and feel a need for direct military action.
So within that narrow area of military pride and perhaps domestic manufacturing, Trump represented a real threat of retaliation and escalation, but beyond that he was pretty much asleep at the wheel.