China is a dangerous and highly-abusive country to work and live in.
Anyone that has ever worked in or around foreign consulates could tell you war stories about numerous foreigners that get victimized in China by schools and recruiters alike.
A purge?
To some minimal extent perhaps.
Based on talking to many people I know, its a mass exodus of people who simply had enough.
Most or all of the people I worked with were credentialed.
I've worked in public high schools and frequently saw teachers being told to teach additional classes as a routine and regular practice.
At current rate in China, there is and has been, an ongoing shortage of teachers.
I've seen, and have been aware of, several schools increasing wages, and despite those wage increases, teachers continue to leave China.
There are so many other places to work at other than China with far less health and safety risks.