Peggy's statement is open to interpretation: was the singer trying to do a Black Texan accent but failing to mask his "Cockney vowels", or was he singing the song with no attempt to disguise his native accent? But if Jim has the story from other sources (other than the article), or is basing his impression on other things Peggy has said, then I'm willing to accept his take on it (a great relief to him, no doubt!).