The orc general was someone who even dared to confront the orc king back during the night of the moon dance. He had also shown his abilities to be nothing like the weakest general as the orcs called him.
He had proven his ability by knocking Berirock away in one move and establishing his position. As much as he hated it, Berirock had to admit that the latter was stronger than him, stronger than any of the orc generals.
On top of that, he was also an orc shaman. If a guy like that said that he had a plan, Berirock could hope that the plan worked. Other than that, he was also concerned about the orcs in the frontlines who were being butchered like livestock by the Gir brothers. Thus he had no other choice but to leave Berigard to take care of the ogre with the crimson horn.