The guy's a well known shitflinger in Utah. Apparently been menacing around the state for years, riling up local law enforcement and getting charged with being a nuisance for decades. So much so that he's on a first name basis with the police and courts in some areas.
He probably rocked up to where Charlie Kirk was due to speak, knowing he could cause some chaos thanks to the heightened tension that comes with political debating. When he saw Charlie get popped, he immediately strolled up to the police as soon as they appeared in order to do a little trolling. Claiming he was the shooter in order to waste their time.