While this is a total bullshit plot twist, it is actually kind of interesting, because the witch specifically said that the petrification eye was the hero's "only" demon eye. Either this isn't a demon eye (because of the cross design and it's some kind of holy/saint eye) and she didn't technically lie, or it is a demon eye and she straight up lied, but either way she intentionally didn't tell MC the whole story.
I guess that means that beyond just loving entertainment, she might have some amount of pride as a "hero" still anyway if it was meant to trap the MC, either that or she thought it would be too easy for him if she told him the whole story, and that wouldn't be as interesting.