"But the general public, not used to the fine distinctions that ethnomusicologists and folklorists make, assumed that they were folk songs due to the style in which they were sung and by the generic term they were used to hearing for these professional entertainers and songwriters rather than the pedigrees of the songs themselves."

BINGO!!! As usage became accepted, the definition changed - just the way the term "folk music" was first brought into usage from the German words.

Most people that are looking to enjoy will not bother checking the pedigree as long as the dog fetches the slippers and brings comfort.