Saving face. It’s what they do. They will NEVER admit what they did was wrong.
From their perspective it was the right thing to do; and, there were no repercussions.
We never apologized for sending reconnaissance planes over Russia, and it was also the right thing to do.
It is all spying with a dash of political theater. It has been going on in one form or another since the dawn of time.
The Chinese probably learned what they already saw on USGS maps.