He could've handled this way better, but noooo, he had to reveal himself, made an enemy out of a noble, and made things much worse. He could've just posed as a god or something with his powers, but we need more reasons for the noble's actions later. He could've disguised it as divine punishment, but I guess either the MC is too dumb to think or the author didn't even consider it in the first place.
And why did it take him so goddamn long to act, bruh