"I mistake"

This morning I saw IZ groaning in pain alone in the hall, holding his stomach. He said he had stomachache and need to poo.

As both toilets were occupied, he had to use the potty. After few minutes, he said he's got nothing.

"I was wrong", he said.

Just to make sure I heard properly, I reflected "You were wrong?"

"Yes, I mistake", he said.