Anyone quote-tweeting this and crying about censorship is a grifter who isn’t interested in the truth. The article grossly misrepresents the study it is purporting to report. This is why the article is labelled as false. https://twitter.com/carlheneghan/status/1329861848573861888
Put another way, the study did not test whether masks protected *other people* from Covid-19 if the mask wearer has the virus. Therefore the claim in the article is patently false and has been flagged appropriately.
Mask wearing is mainly about protecting other people in the community from droplets emitted by the person wearing the mask. Though in this study some wearers appear to have been protected too.
Facebook are entitled to attach warnings to articles which are pushing false information during a deadly pandemic. This is not censorship. The article is still up, it simply comes with a health warning attached.