SPOILERS

I was walking through the desert area and a bunch of people burst out of the sand to talk. By pretending to be someone else I was able to get their prisoner transferred to me. They left and when I tried to leave the area, another group appeared and walked toward me. However, they disappeared before they got to me and now I have a slave who doesn't talk and presumably a quest I can't complete. What was supposed to happen?

EDIT

I loaded a previous save and turns out if the second band doesn't disappear you fight them, after which the slave wakes up and you have a nice chat and gain xp and he makes like a tree in autumn