It depends on what the mask is supposed to do. In the hospital it is to keep one from being exposed to infectious body fluids. In the natural environment it is supposed to keep viruses out. Clear empirical evidence now shows that the mask is meaningless for casual wear. The NEJM recently published a strong controlled study showing that mask wearing increased chances of a positive test result, which just make sense if you think about it, and the opposite result from what we have been having drummed into us. There is no “science” that supports mask use among the general population.
He's taken an elephant's worth of data and distilled it down to a dinner plate sized portion.