There was no lie in the fact that he was a Devil God.
But he was a newborn Devil God.
He could be killed by devils if he was caught off guard.
Of course, they didn't know that.
And with his acting, he reinforced his image as an omnipotent god in their minds.
After he explained himself, the variants stopped doubting him. However, if they had pressed further, he would've just killed a few of them to make them realize he held their pitiful lives in the palm of his hands. That would have made them shut up and act subservient to him.
"Then let me do the honor," Dris explained to Val, "The cave walls are embedded with ancient runes our ancestors left behind for us. These runes can harness the energy stored inside a mana stone, using it to generate a protective barrier. As long as we ensure a consistent supply of mana stones to these runes, the barrier will persist even if it's sufficiently damaged."