It' probably futile to hope that this doesn't open a "what is folk music" thrash, but there's a category of enteertainers who used acoustical instruments and polished but relatively plain arrangements who were/are someplace on the edge between "folk" and "pop." The right-wing groups in the Studio 360 piece were mostly in that category, just as groups like the Brothers Four and New Christy Minstrels, who were considered "folk" to the general public.

It's a perfectly legitimate genre, but it's a different genre from traditional folk musicians or revival performers who use traditional material and forms.

In this platform, where we are all presumably more knowledgeable about the shades of difference, it's fair to argue that those righties were not "folk musicians." But neither were many other, more visible and more popular performers who were called "folk musicians" during the same period.