It's one of those random land events, that only happen when the player is accompanied by crewmembers like soldier patrol, enemy soldier ambush, native ambush and tavern brawl.
When the I enter an area, there might be a pirate ambush. In ealier versions the pirates attacked everyone and fough to the death (theirs or everybody else's). Now they only attack the soldiers in the area (at least in a town, I haven't experienced it in the jungle yet) and then stand still, when all of those are dead. It's very like the behavior, my own crewmembers showed in an ealier ambush situation: fight the enemy and go completely inactive, when said enemy is gone. I can't talk to them. But they do react with violence if I attack one of them.
When the I enter an area, there might be a pirate ambush. In ealier versions the pirates attacked everyone and fough to the death (theirs or everybody else's). Now they only attack the soldiers in the area (at least in a town, I haven't experienced it in the jungle yet) and then stand still, when all of those are dead. It's very like the behavior, my own crewmembers showed in an ealier ambush situation: fight the enemy and go completely inactive, when said enemy is gone. I can't talk to them. But they do react with violence if I attack one of them.