Nobody seems to be tracking the origin point of travelers. If an asymptomatic carrier from Wuhan took a train or flight to Beijing last week (exposing other passengers to the pathogen) and then boarded a flight from Beijing to SFO (San Francisco), the presumption would be that the traveler is from Beijing.
Tens of thousands of people have boarded flights in China over the past month and deplaned in international destinations. The likelihood that some consequential percentage of these travelers originated from Wuhan, or were infected by someone from Wuhan, is high.
It's basically impossible to thread these three points together and not conclude that a massive expansion of the virus is about to manifest in dozens of international destinations.