Along with misidentifying food as a threat, there are several mood-modulating and hyperactive impacts to food avoidance for those with eating disorders that non-eating disordered people do not experience.
While the rest of the non-eating-disordered tribe was listlessly and fractiously lying around the dying fires feeling sorry for themselves that there was not enough food to eat, the eating disordered tribesmate was feeling ready to take on the world.
She went out foraging. She felt calm, a bit buzzed and most definitely clear-headed. If she managed to score food for the tribe, then the tribe (and its genes) survived.