China's claim is that anything that is being done is being done to combat islamic fundamentalist groups/extremists. This seems to be backed up by international support from Muslim countries.
Genocide claims were always unfounded. However, no matter how nice the guided tours of reeducation facilities look, they are still in effect prisons, and we of course don't know about the things that we aren't being shown.
If your position on the topic is anything more than "They may or may not be treated that good", you have information that nobody else has.