I read it that the person got sick after the visit to Wuhan but recovered from that before the visit to OP. Hence 3+ days should be enough to rule out a possible infection of OP with whatever the scientist had.

Since they traveled to Wuhan in December, from then to last week, that would've been more than 24 days, so in case they did not get sick yet and I read that wrong, it should also be pretty much impossible, since that would be the longest incubation period of ncov by quite a bit.