Sinister supporter: nobody suggested jazz originated with English folk song, which would be a remarkably silly posaition to hold(though certain New Orleans tunes, St James Informaryu and Didn't He Ramble, for example, did see the light of day in England before they crossed to Louisiana).
No, what the statement said was very clear, and absolutely correct. That if you study the origins of jazz, you will be lead to American folksong. And that if you study the origins of American folksong, you will be lead to English folksong. Now, which bit of that statement do you find difficult to understand, or disagree with?