There’s a whole body of case law concerning “free speech fora.” If he’d been on the sidewalk, there wouldn’t have been a problem, but to be on the grounds of a government facility doing this is no different than if they’d come into a store, a courtroom, or your home and done this.
To be on the grounds of a government facility is not trespassing, which is what these men are being charged with, especially considering there were customers lined up waiting for the DMV to open who were not charged.