Likely confirmation bias.

Even if no one was sick, straight-up, most of those tests have a 1-5% failure rate. Going on the low end, they're all likely to go home and test, you're going to get a couple results. On the converse side, CPAC ain't testing unless they're getting hospitalized, which they weren't. So you could have an outbreak but it goes unnoticed because, you know, it's just a cold.