Wonder if his toe got caught in the cage.
I doubt it...
He most likely went for a leg kick and ended up hitting the guys knee and it just broke off. Gotta hit something pretty solid with that and I doubt it was a head kick because most fighters are aware of how to do that without getting your toe broke, not to mention being stuck in the cage.
"MMA and Muay Thai are similar in a few aspects, such as the fact that their is no traditional belting system - only a list of people you never want to have to fight." - Kenny Florian