That quote seems a bit "iffy" to me.
Bill Broonzy died in August 1958. I believe he last played England in 1957.
I was taking guitar lessons from Peggy Seeger in 1959 at the premises of the WFDY in Islngton. A fellow pupil was Wizz Jones. If Broonzy was playing a lot like Wizz when he was here I doubt whether Wizz would need to go to Peggy for lessons two years after Bill's last visit.

I'm not knocking Wizz but I don't remember him being that accomplished at the time. If he was I might have gone to him for lessons instead.

I don't think anything went wrong it's just like the song says "Time Changes Everything".