Not the person you replied to but but some of the biggest pop science is based on this misunderstanding of how lab science applies to the real world. Remember Bt corn and the monarch butterflies? Time ran a watered down version of the science basically that bt corn pollen is the leading cause of monarch population decline. Ok the study they cited didn't say that and time's target audience is a) not inclined to read the actual study and b) not scientifically literate enough to understand it.

Now to apply that to masks. Is woven cotton fabric capable of stopping a free floating virus? No, but that doesn't mean there aren't real world factors at play that cause masks to reduce the spread that aren't present when testing if cotton fabric blocks viruses. Do masks stop droplets, people from touching their face, picking their nose? Do they serve as a reminder that there is a pandemic and cause people to alter their behavior/hygiene in other ways?