This is actually not a screenshot, but I have made a great discovery! Forgive me if this has already been found out.
Remember the screenshpt earlier at the bottom of the map? Well, I was curious what would happen if I popped barbs from a hut down there. So, I decreased it to 2 tiles, one with my Settler, Worker, and Warrior, and the other with the goody hut, and for the greatest chance of popping barbs, played it on Sid (90% Chance of barbs). I popped it 10 times, and didn't get barbs once- just maps and warriors. The chances of that happening normally are (I think) 0.000000001%. So I guess that's another requirement for barbs to get popped from the hut: "There must be 3 empty land tiles that they can spawn to."
EDIT: Oopsie! I forgot to give myself a city, which is one of the requirements. I'll have to go do that.
EDIT2: Nope, I gave myself a city (which wasn't one tile from the barb camp) and still didn't get barbs after popping it 10 times on Sid.