Here we go again!
"Borrowing" folk melodies and bits of lyrics has been going on since Adam!
Woody Guithrie did it all the time. For example, Woody used the melody "Pretty Polly" for "Pastures of Plenty" and Dylan used it for "Hollis Brown".
Interestly, when Alan Lomax made field recordings of Muddy Waters back in 1941, Muddy sang a song which he claimed to have written, but Lomax knew that song "belonged" to another singer, but when challenged, Muddy said that he had the made the song is own by rearranging the verses and mixing in material from other songs.