The scrawny humanoid demon had done his best effort, waiting for the perfect moment when the forest front needed help, sending the muscular humanoid demon away so that he could have himself a leeway to do his other plans such as preparing the rune formations that he might need, then the most troublesome of them all, herding the demon horde to go into the forest base direction.
The demon horde method might not work if the scrawny humanoid demon had sent them to anyone random, but he knew the muscular humanoid demon well. The muscular humanoid demon would have taken the horde of demons as a challenge, and with the base being attacked, there would even be more reasons for the muscular humanoid demon to stay and fight the demon horde.