This is not how the placebo method works.
Let's say people were not social distancing and were without masks - and, thus, were exposed to a potentially higher virus load. Your placebo group would then end up with 180 infections and the treatment group with 10 infections. (Maybe - it's a prediction based on a sample.) Your conclusion would not change unless it can be demonstrated that those in one group somehow got a higher exposure.
Things to keep in mind:
1 There is no scientific study proving that someone wearing a mask (and distancing socially) would get a virus that is somehow different from the virus in others.
2. The participants in the study are being tested using PCR tests at multiple points in time. While a lower exposure could result in less severe symptoms, the PCR tests would still catch the virus with a high accuracy as long as it was transmitted.
3. The mask mandates and social distancing measures will likely be removed only when the virus transmission rates are already low.