I am just not sure I buy that given the high R0 (I've seen 5.4?) and the fact that the Wuhan outbreak and subsequent Italian outbreak have done far greater damage than anything CA experienced plus it would have spread throughout the US first if CA was the epicenter. Of course it is possible it mutated from whatever hit people in CA last year (and I've heard people go back as far as February of 19) but to me this seems like a lot of wishful thinking.
1) Is very contagious (high R0)
2) Is frequently asymptomatic
3) Asymptomatic people are contagious
4) Is rampant in a country from which 8,000 visitors a day come to the U.S.
could somehow just fail to get a foothold in the U.S. for months on end. This thing was going in Wuhan by November at least, and travel didn't get shut down until the end of January. That's maybe 2-3 months worth of travelers (so on the order of 500,000+ travelers!) and no foothold? I can't make that add up. So I'm inclined to believe that either some of those assumptions are wrong, or it has already been here.
If it's already here, then the question becomes why didn't we see it?
The antibody tests described in that ABC news article will basically tell us whether the better question is "Why wasn't it here?" or "It was here, why didn't we see it?"