He was riding with a few people, passing a buffalo that was off the side of the road, eating, when he heard a 'snort' and the pounding of hooves.
He glanced back to see the buffalo coming up on his rear wheel.
Needless to say, Jeff poured on the steam, and managed to 'drop' said buffalo.
I contacted David Wilborn, the artist behind Urban Jungle and asked him if he could draw a picture commemorating the chase. He did an AWESOME job!