Prior to coming here, they primarily ate small lizards and fruits.
They were allowed to immigrate to this country by abandoning their old gods, and exterminating as many giba/kiba as possible. Additionally, harvesting anything a kiba eats is forbidden, since if mountain resources get scarce, they begin attacking farms for food. These super boars breed like crazy and get super big; put simply, the acquisition of all the meat is a waste of time. Big clans are expected to exterminate several a week, and no matter how many they kill, the population never drops significantly. Before they arrived, giba/kiba had a reputation for being nasty. Despite that, the poor immigrants had no choice but to eat it anyway. So it was widely regarded as an unsellable product only good for its nutritional value.
To make matters worse, the noble of the tribes only did the minimum amount of interaction with the country they moved in to, selling their horns/tusks to buy necessary products like veggies/fruits/wine/salt/utensils/weapons/etc. The ignoble abused their race's superior strength and harassed peasants in the local stone city, which created even more divide, racism, or fear. The noble(as in honest and good to their beliefs) o f the tribes ended up getting labeled with derogatory remarks like kiba eater or such, and rumors spread that if you eat kiba, you become mean-spirited savages. They didn't let it bother them and wore it like they owned it, since they felt they didnt need the country anyway, and the nasty meat was what was keeping themselves and their families alive anyway.