Riddle Number Twelve

Police chief Carl got a call from a man who claimed to be the victim of a crime. The man said, "I was just sitting on a park bench, minding my own business, when this guy came up and snatched my wallet! I couldn't see his face, but I know he was wearing a black hoodie with the hood up. I tried to chase after him but he was running too fast. I remember he had green eyes, too. It happened way too fast to get anything else."
Carl was suspicious, so he put the man on hold and told his assistant what had happened.
"He was convincing, but he slipped up," said Carl. "I know he's lying." How?