So, I read the study and I don't think you can make any conclusions based on those results. Most people get infected at home, so if only few people were masks, a handful of participants wearing masks outside does not help limiting infections at all.

During the study period (3 April to 2 June 2020), Danish authorities did not recommend use of masks in the community and mask use was uncommon (<5%) outside hospitals (22).

Eligible persons were community-dwelling adults aged 18 years or older without current or prior symptoms or diagnosis of COVID-19 who reported being outside the home among others for at least 3 hours per day and who did not wear masks during their daily work.

So they are at work, were no one wears masks, are apparently socially active and surround themselves with people who don't wear masks, and they are at home with people who also don't wear masks. Really, what is the point of this study?