I saw the same pirate in Skull Island. It looked like she was going to Buster Crab's cave. She was moving slower then the normal speed while moving, and she had no visible name. Then I saw another one in Flotsam, and then I saw the Achaea one.
My theory is that they are some kind of road signs. They say, "Hey, look over here this way. Something is over here. Follow me." Where one pirate goes, another one will follow because there might be a quest or treasure.
I remember jack saying somewhere that they just put those in the game to spice it up make it look more real
Cause nothing looks more realer than a few animal companions walking and talking, all the while, fighting with you in battle to defeat a robotic army, when you're only a kid, probably 15 at most. ... lol, I'm just joking, mate. But I just couldn't resist when you said "real," hehe