I can't see a problem with a magazine informing readers of the origin of their printed material. Take any number of people who have learned a song aurally from one source and I would bet that in a very short time there would develop either naturally or by design an almost equal number of slight variations on the original, it's known as the folk process. I would assume that the magazine in question was merely clarifying that that was the way a particular singer performed the song.

Is it not still common practice at a folk club for a singer to inform the audience the origin of their version of a song?

I can sympathise with the Drummer above if he has written songs and not been credited but he should not confuse his writing of modern songs with the performance of traditional material which I thinks is what is being dicussed here.