It was before the first confirmed cases, but no one was looking. Over 700K people travelled from China to the US in December, January, February. Many of them came directly from Wuhan. Given what we now know about asymptomatic spread, it stands to reason this was in the US much earlier than the first detected cases.

That said, I agree that even now a vast majority of those tested turn out not to have the disease, and back then it was even less likely.