Thank you for the explanation. That's what I thought.

In the "old days" people weren't so concerned with being truthful about the sources of songs, etc. It goes right back to the beginnings of folk song scholarship with Achim von Arnim's and Clemens Brentano's "Des Knaben Wunderhorn", one of the first European collections of supposed folk songs and poems. "Supposed" because they and their friends (including Goethe) enjoyed smuggling in poems of their own and they weren't and didn't want to be scholars.

And there are (substantiated) stories about well-known performers claiming that music was traditional or from composers of the past whereas they wrote it themselves or had someone write it for them.