Unfortunately masks are most effective when the person with COVID wears them, rather than people who are trying to avoid COVID, but human nature is such that people with COVID (ones who go out in public) are often ones least worried about it so least likely to wear a mask in the first place.
I had a similar experience where I went to a conference and masked up religiously around groups only to catch it anyway while my colleagues didn’t mask and didn’t catch it.
Sometimes you can do everything right and still fail (paraphrasing Picard).
At the end of the article, which is already a litany of clownish buffoonery, it states that after destroying (effectively) the MRI machine in order to retrieve the rifle, he failed to retrieve a loaded magazine. So it was just left on the floor as they left.
Edit: autocorrect had changed it to clownfish