With asymptomatic transmission the virus likely would have spread unnoticed in the town that was encroaching on bats for a while before someone brought it to Wuhan.
The concentration of early cases in Wuhan, hundreds of kilometers of away, would imply that the asymptomatic traveler(s) only traveled to one city, and didn't infect any other people along the way.
It's possible, but you have to consider the probability of all these events, hence the Bayesian analysis performed here.