Don't remember the particulars, but he'd heard about Houston's offer on the radio and found one of the few busses which Mayor Nagin hadn't mustered into the underwater zone, so just put two and two together and took action.
He was not 14. He was 20 with a criminal record longer than your arm and wanted by the police. He stole the bus to keep from getting picked up by the cops and took others with him to Houston so he wouldn’t blow his cover.