Yes, I'd far rather listen to Nine Inch Nails than bluegrass too. But whatever point you are making is far from clear. Bluegrass isn't music 'rooted in a tradition' but a relatively recent US invention (by Bill Monroe, principally) combining elements of a number of evolving traditions brought into a specific US region by a variety of immigrant musicians.

What Jim Causley was referring to was performing music wholly rooted in the English tradition to (mostly) English people at a (predominantly) mainstream festival and surprising them greatly.

We would seem to be two very different nations divided by a far from common language by an ever-widening pond. That in some ways makes me feel better.