I think this is merely a new version of "all music is folk music", but with a more poetic slant, and no mention of horses. I'm not surprised McGrath is in favour, I seem to remember he was always the First Horseman of the Definition.
    No, sorry, I dont buy it. "A nightingale sang in Berkeley Square", for example, is a perfect exposition of "what happened"(though possibly fictional). But wild horses will not persuade me that it is a folksong.