"Just like I thought, they're gonna defend those demons." The man said, looking at the scene from far away. He is currently relying on the eyes of one of his summoned creatures in order to get a clear view of things. Through this, they can't detect him and, even if they do, he could simply release the summoned creature.
As he did this, the man meditated within the same cave which Jake tried entering. The goblins killed by the javelin user were actually summons made by him in order to ward of any intruder. If these are killed, he simply needs to release some of his mana and, anyone would back away immediately.