Maybe it helps to understand that Taiwan's Air Force and the PLAAF have been duking it out since the late 1940's.
In the 1950's and 60's, Taiwan's AF was VERY aggressive when it came to flying over mainland China and exchanging gunfire with the PLAAF. They mostly flew (then current) USAF fighters and recon aircraft.
Things have cooled down since, but both sides continue to push the other side's buttons. If it helps, both sides file flight plans with the other prior to taking off.
