Folk is a term used by the semi-academics that dwell there/here and describes whatever they want it to mean.
To be fair, I don't think it's that vague. They clearly use the term to describe their particular kind of popular music from their particular culture. That's pretty specific. I note that there is little talk of Chinese music in this context, and even (as I pointed out at the beginning of this thread) Danish "folk" music does not fit the current English/American use of the word - and Denmark is only a few miles away.