The point is that a test that has a guarantee like "out of 100 people who test positive, only one will turn out to be negative" (99% specificity) can have an ar

The point is that a test that has a guarantee like "out of 100 people who test positive, only one will turn out to be negative" (99% specificity) can have an arbitrarily high false-positive rate when applied to the whole population: if a condition affects 1 in 10k individuals, then out of 10k individuals that take that test, 100 will be positive, but only 1 will be a true positive. The rarer the condition, the more specificity you need in your test to have a low false positive rate.