Even if they were testing people that were all externally known not to have COVID, if only 0.5% of people are testing positive, that's the false positive rate.

Even if they were testing people that were all externally known not to have COVID, if only 0.5% of people are testing positive, that's the false positive rate. All the data we have indicates that false positives on PCR are extremely rare. The only place it gets fuzzy is the definition of positive. People who were previously infected can test positive, and people with very mild infections can also test positive. People who have never been infected though essentially do not test positive.