Revealing mistake: After Evolet got hit by the arrow and presumably dies, D'leh is staring at a mammoth. Behind the mammoth, you can see that the background is a picture.
Revealing mistake: In the scene where D'Leh is chasing deer across an open plain, there is a row of 4 to 6 cars with headlights on in the distance coming down a gentle slope.
Answer: It is explained that he decided not to wait for the last hunt and left to find another way to feed the tribe. He left in secret so that others would not follow him abandoning the tribe.