True, "Articulation and good diction do not necessarily run counter to 'regional mannerisms or colloquialisms,'" but I think what Dyer-Bennet was referring to here was the self-styled "folk singer" (urban born and raised) who characteristically tries to sing as if he or she had just ridden into town with a load of turnips. That is, someone who, to one degree or another, tries to pass himself off as if he were a "source" singer. I'm sure we all know a few of these (and a couple of them have managed to acquire a measure of fame).

I knew one singer personally (born in one big city and raised in another) who generally dressed quite nattily, but whenever he had a singing engagement, he would change into a non-descript pair of jeans with a rip in the knee and a sloppy shirt that should have long since been consigned to the rag-bag. Tried to look as if he'd just been thrown out of a boxcar into a muddy ditch! That always struck me as more than just a little phony.

Dyer-Bennet, who considered himself a modern minstrel rather than a folk singer, had nothing against affecting a regional accent and using colloquialisms if they were an integral part of a particular song, but he never tried to pass himself off as anything he wasn't.

Don Firth