And even if they state that, they can't just take or search someone's property. Maybe if you literally signed a contract allowing that, but I am uncertain if the right to not be stolen from is even possible to sign away.
If I tell someone that if they enter my house, I am allowed to rip off their clothes and tear or burn them... I am still not allowed to do so even after they entered my house. I can demand they leave the premises, but even if we add the axiom that they actually said "sure" to that demand of mine, if they changed their mind and revoked their consent after entering I would suddenly find it illegal to do so.
Yea, generally stuff like that is a thing, more so if you're putting a person into a state like that..
In these cases, the purchase of entry to the venue is the same kinda deal as when you scroll past all of the EULA text to click "I Accept" - In this case, kinda like how if you're toxic in an online game, your account status can just get straight up revoked.
In this case, they didn't smash the camera and they did so under the guise of "Let me make sure it's okay for you."
Is it right? Nah. Did it resolve the situation? Yeah.
Last note on all this, keeping in mind that this isn't directed at you personally or anything (Sorry for the reply, honestly, was just adding to the conversation) - This is a manga. A world different from our own that exists in its own state unless otherwise stated by the person who imagined and wrote the story that they're telling us. They can do whatever they want.