The professor explicitly cut ties with the student because she was afraid to lose her ability to get a visa for China. It's unclear how she came to this conclusion, but I don't see how she can conclude this just from a message she got from a student in Canada. Chinese authorities must have made it clear at some point that they are ready to punish either this or any slightest misstep like this. And it's really an insignificant incident: someone who is not officially her student, has basically no followers because he just created his account, tweets a little and deletes everything as soon as the professor finds a problem with it.