No reason you should listen to me in particular (no doubt I have made egregious statistical errors myself in my research), but a good place to start might be https://en.wikipedia.org/wiki/Binomial_proportion_confidence... or, as others have posted, it's worth listening to Andrew Gelman (unlike me, a statistics expert) about this! https://statmodeling.stat.columbia.edu/2020/04/19/fatal-flaw...

Essentially the problem with the study is that the bounds on the false positive rate of the test used was such that the data are completely consistent with all of the positives being false positives.