Given that Ramplod is years past his best and hasn't looked impressive at all since KOing Wandi and even then, he didn't look great up until Wandi hung his chin, and Ramplod came in over weight and with an injury, I don't think it was an upset.
For me, by far the biggest upset in combat sports history was Bob Sapp beating Ernesto Hoost in their first fight. Hoost is arguably the greatest kickboxer of all time, Sapp is an embarrassment to all of professional sports.
Anyone got a bigger upset than that?