Sorry if I got it wrong, but I'm pretty certain that I didn't. As I understood the story it was a cockney stab at a black Texan accent that pushed Peggy off her chair.
Not the way I read it. Peggy said -
I knew what the song should sound like and the manner of delivery and the insertion of Cockney vowels into a southern USA black prisoners' song just sounded funny.
It was singing a black Texan song in a cockney accent that was the problem.