Here's what it could be. There is song; a poet imitates the song form and creates the poem. The composer sets the poem to music, and there is a new song.
But this new song is different from the original, anonymous, popular song. In 2 ways. Now the text comes first, and is set to music. (In the original form of a song, music and words both come first, in a way. There is no necessary precedence.) Secondly, there is a popularization of a text that belongs to the cultured tradition.
