I think this warning is mostly in response to dual (US/China) citizens who have had their US citizenship not recognized by China, which then handles them according to Chinese law. I don’t know much more about the warning than what is written at the link you shared, but if you search on Google for more information on this, I’m sure you’ll be able to find some useful info. In general the atmosphere for Americans in China has gotten more tense in recent years. If you are mindful to adhere to all of the laws of China, I wouldn’t expect to have any problems.