Anarax
Master Black Belt
I'm willing to be that the scream he made was not the same scream he would have made if he thought his life was in danger. Sort of like how we laugh at a guy screaming on the roller coaster, but we don't laugh when we hear a scream that sounds like someone is in real distress.
The researched talked about our ability to recognize screams.
At the time he thought his arm was broken, thus he made the same scream that he would've made in the multiple attacker scenario.