Sounds very familiar. I saw him talking about it in a documentary on the BBC. I have the inkling it might have featured Mississippi Fred McDowel a lot, or Seasick Steve (because he did a some driving of Fred to gigs). I do remember JS saying he saw MFMc at Newport FF and then he was billed at a Folk Club in Greenwich Village and JS said "could it be the same person?". After the show JS asked questions of "Mr McDowel" about guitar technique. Fred had said "I seen you looking at me".

Somethings did stick in my mind.

Seasick Steve video (Not available) Bringing it all Back Home
BBC iPlayer find the same video when you search for Fred.