That was still very early. The alarm was raised by that doctor in China who was Wuhancided, before it got widespread. Wuhan was quarantined on Jan 23. So there was only a week window from mid January until most of the afflicted were locked down. Then the President started halting travel (and got chastised for that) and airports started screenings and so forth. So you can credit prompt action by Trump for part of it. Still, it did get out to the rest of China, HK and some other places. And it is clear that the incubation period can be widely variable. And the test kits suck, with massive numbers of false negatives.
The success, so far, has been due to very aggressive containment efforts (although I would like even more). Some more successful than others. As long as we can stamp out any given outbreak before it gets completely loose we’ll be okay.
And Hong Kong, a month later has fewer than 100 cases. And students returned through the end of Jan to American colleges.