I'm sorry, but we've known that masks work for literally a century. They were also recommended during the 1918 pandemic. There is a wealth of literature on this topic; it is scientific consensus.
It's great that you're thinking critically about the ways that this individual study might fall short, but trying to poke holes in a study here or there does not undo the (literally) century of research underlying the efficacy of cloth masks in preventing the spread of airborne illnesses (or epidemiology in general).
This is the thing that truly drives me crazy about the political deadlock, and the replies to this comment are a good example of it: Democratic politicians propose a common-sense, obvious measure that would be objectively good for society (e.g. healthcare; slowing down climate change; addressing a global pandemic ravaging our country; providing money to the people now out of work due to the economic recession caused by the pandemic). In turn Republicans (politicians and right-wing pundits, that is; not referring to constituents), respond by fighting tooth and nail opposing it, using nonsensical buzzwords and ad hominem attacks on whomever sponsored the bill, and make it one of "The Issues" for political points, further subverting any real, meaningful discussion on policy issues. I've watched the GOP degenerate from "kind of annoying, but valid counter-points" to "blatantly obstructionist" staring with the Tea Party during the Obama Admin, and only getting worse from there.
Today there's the "Let's actually do our jobs and keep the country running" party and the "Let's destroy our country and blame it on the other side because corporate lobbyists pay us to do so" party. And somehow we need to find common ground and unity when the other side is more interested in bullying and obstructing the Democrats than it is trying not to kill another 200K people. There's compromise, and then there's calling a spade a spade.
To be clear, I won't pretend the Dems are fine (and if there were a way to vote third party without throwing away my vote, I would do so in a heartbeat). But the Democrats aren't even particularly progressive anymore. Bad-faith concession after bad-faith concession to the GOP over the course of decades has slowly dragged the Democrats to the center, while the GOP's actual extremists making a mockery of our democracy have the gall to label providing healthcare as the real extremism.
It's great that you're thinking critically about the ways that this individual study might fall short, but trying to poke holes in a study here or there does not undo the (literally) century of research underlying the efficacy of cloth masks in preventing the spread of airborne illnesses (or epidemiology in general).