These articles don't have much convincing info in them if you dig deep. This study referenced here is another 'correlation + speculation' paper:

Association Between Universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers

Another one looking at time-frames and assuming positive trends are from mask-wearing. It's sciency hand-waving at it's finest. Though the paper does acknowledge the possibility, of course you don't see those details in the WSJ article:

Universal masking at MGB was associated with a significantly lower rate of SARS-CoV-2 positivity among HCWs. This association may be related to a decrease in transmission between patients and HCWs and among HCWs. The decrease in HCW infections could be confounded by other interventions inside and outside of the health care system (Figure), such as restrictions on elective procedures, social distancing measures, and increased masking in public spaces, which are limitations of this study.