Many, many links in that article, but in the only study I see, this is not an experiment, it's observational study.

There are lots of reasons to believe wearing masks might be correlated with other mitigating behaviours (hand washing, going out less, etc), which would also reduce contact with the infected.

Also, I see no mention of studying possible side-effects of universal, permanent mask wearing, which makes this study irresponsible at the least.