Here’s why:
It would mean that this did not really come from China but is a new virus at large.
I do not believe that. It makes no sense. This person lives in the San Fransisco area, Solano, 54 miles from SF, could have had contact from someone who’s come back from China with no symptoms, no disease, and that’s it. SF area has a huge Chinese community.
There is very little to no chance this just happened to appear out of nowhere.
They’re not telling the truth because they do not want to isolate the Chinese community there, but this is not the time to not tell the truth and claim this just happened and we don’t know how. Contact with someone who came from China with no symptoms is a more believable option.