This achievement is supposed to pop after you convince Wogah (One armed guy) to join your village after you complete escaping from the cave that he pees on you in. He abandons you and you escape that cave in order to come back up and around to confront him again, at which point he'll join the village.
This is another achievement that after I met the conditions for the achievement failed to pop as I've convinced him and fully upgraded his hut as well to no avail.