This is baffling. The dude was arrested on an unrelated warrant after he was spotted in surveillance video and picked up. During the interview he admitted to setting the mailbox on fire, but claimed it wasn’t politically motivated and he just wanted to be arrested. If he already had a warrant he could have avoided additional charges and just turned himself in. This is Florida Man level shit.
He might not have known he had a warrant. It's not like you get told until you have an interaction with a cop. Most people with warrants literally find out about them in jail.