Curly Fletcher was I think a friend of John Lomax the tune does not have statements on if it was original or not. Montanna Slim wrote many Strawberry Roan in the 1920s and throughout the next decade. In 1944 Woody Guthrie wrote his song There's More Pretty Girls Than One. He might have met Curly and John in the studio and liked the tune so much and decided to set it to the same or very similar paterin tune. This could have more writers from the USA and Britain to write their own words from the early 1950s when the folk revival was going on formant.