I’m pretty sure that ‘gunfight’ is a broad term for when two people are ‘fighting’, whether it is with a gun or not, and you cannot determine who the traitor is of the two of them. In this situation, you don’t know who is the traitor, so by joining the fight you have made yourself vulnerable to a punishment. However I think the punishment is harsh as the rule isn’t very well explained in the rules (this aspect of it). I feel this could have been resolved with a simple talking to.