That really depends on the tests and time period. False positive rates depend not just in the test but also the percentage of population infected. Unfortunately many people where diagnosed based on symptoms or a single test which was inaccurate. At the time telling someone to self isolate based on an inaccurate test and only preforming more accurate testing if they got really sick was considered acceptable.

In a study of 14 of the approved tests, one of the tests gave false positives more than 15% of the time, and three others gave false positives more than 10% of the time. https://www.sfgate.com/coronavirus/article/which-COVID-19-te...