Archie Green's book "Only a Miner" also has a good summary of Charlie Bowman's role, based on interviews he conducted with Bowman in 1961.

Bowman told Green that when he was a teenager, the black railroad crews came through his town, and he spent a lot of time hanging around them to listen to their music. He learned the song at that time, then remembered it twenty-two years later in the New York studio where Brunswick 177 was recorded. In Green's words, "Nine-Pound Hammer stemmed directly from locutions and a melody used by black railroad-construction laborers early in the century."

This is confirmed by the 1926 Gordon recording, which features the line about the hammer killing John Henry, which is also one of the verses of Bowman's song.