He's not suggesting that it was widely circulating in the U.S. He's suggesting that someone coming off a flight from Wuhan might have passed it to him. At the end of December, we know for certain that there were numerous cases in Wuhan, so it's entirely possible that he caught it, passed it to his family, but they never infected anyone else.
Now would I bet on this? No, but it is entirely possible without resorting to anything that's not established scientific fact.