That sounds ****in horrible! I think i saw frank mir break someones arm using that move!
He broke Tim Sylvia's arm with an armbar. He broke it in the center of the forearm though. Tim's elbow slid out and the pressure was then applied to the forearm, and it snapped.
Most times if you can properly apply an armbar it's going to pop at the elbow and bend backwards. It's more often than not an actual break, but rather the capsule in the elbow giving in to the pressure kind of like your shoulder being dislocated and coming out of the socket.