This goes contrary to what other studies have found. In the Stockholm metropolitan area they found that 2.5% percent of the population was infected [1]. In in a community in Germany, which was the epicenter of the outbreak for a time, they found that 15% of the population tested positive for antibodies [2]. In Iceland they found that 88-93% of the infections are undetected [3].

[1] https://www.folkhalsomyndigheten.se/nyheter-och-press/nyhets...

[2] https://www.land.nrw/sites/default/files/asset/document/zwis...

[3] http://www.igmchicago.org/wp-content/uploads/2020/04/Covid_I...