One of the authors here was the lead on the early Stanford antibody prevalence study that had numerous issues: https://statmodeling.stat.columbia.edu/2020/04/19/fatal-flaw...

It also did not report a possible funding conflict: https://www.buzzfeednews.com/article/stephaniemlee/stanford-...

Have not picked through the statistics cited in the article yet, but I'd be careful with the conclusions derived from them.

Edit: Direct link to Buzzfeed article.