But then I'm just a toothless old pedant who happens to believe that words have meaning ...

Words do have meaning. They mean what people use them to mean. That's what it means to mean. If enough people use "folk" to mean "music played on acoustic instruments" then that will be the -- or at least a -- meaning of the word "folk". There is no "right" definition of a word that gets locked in time forever. That's not how language works, except maybe the French who have language gatekeepers. The English language does not.