My understanding is that it was Big Bill Broonzy, not Louis Armstrong, who cracked wise about never hearing a horse sing when asked if he had just performed a folk song.

The last folk revival happened after the excitement about oldtime music that O Brother Where Are Thou? generated. At least so I judge, as a longtime CD reviewer, from how many trad-sounding CDs were showing up in my mail in the subsequent two or three years. Now, sadly, we're back to "folk" as singer-songwriters oblivious to the tradition.