American blues singer Big Bill Broonzy (1903-1958) explained in a 1953 performance (and probably earlier):

“Some people call these folk songs. All the songs I’ve heard in my life was folk songs. I never heard horses sing one of ‘em yet.”

A 1956 newspaper attributed the remark to American jazz musician Louis Armstrong (1901-1971):

“Louis Armstrong, who’ll star on an NBC spectacular this Monday, was asked what he thought of folk music. ‘Folk music?’ Satchmo repeated. ‘Why, daddy, I don’t know of no other kind of music—I never heard a horse sing a song!’”
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Each to his own, I guess ;-)