The reason the man was arrested is because, without obtaining proper authority he decided to do the equivalent of make bomb jokes at the goddamn airport. it was there job to find potential threats and they found one, the man painted a target on himself and, because that's what security is supposed to do, they nabbed him.
That being said, I think 50+ officers is overdoing it, and the security for the G20 was overkill. The man should face charges of 'mischief' or otherwise, be given a slap on the wrist, and everyone should make a big deal about it. They have to scare off people like him, the ones who want to dick around with security(for good intentions or bad). It causes a huge waste everyone's time and resources.