This is a long-range hunting party that left the tribe just a day ago. Every so often, the Chief himself leads the team to hunt.
The prey is not only ferocious beasts but also natives from other tribes. In their view, nothing is inedible. Rather than risking their lives hunting large beasts, killing natives is somewhat easier. As for cannibalism? The natives still in the Stone Age feel no pressure about it at all. After all, morality has not yet been born; they simply follow their instincts to survive.
The tender-skinned Fang Zhiwen and her companions are clearly a tasty treat, and the Chief would naturally not pass up these seemingly similar fellows. Upon the scout's discovery of them, he immediately launched an attack.