I wonder what the legalities are if someone buys a ticket to a show or an expo and is refused entry if they have not done anything pertaining to those events that was not breaking facility rules or breaking the law?
Most likely not.
Usually events are held in private facilities, even the Olympia, for all it is, is held in a venue that someone owns.
Usually there are stipulations on the ticket, and if you break them, you can be asked to leave.
If the rumor is true and Mel is wrong about Aaron being asked to leave (There is someone who is posting saying that they saw the entire thing go down and Aaron left his seat and went up front, where he was told to go back to his seat, once seen) then the whole thing changes.
If he moved from his assigned seat, he can be asked to leave, or escorted out for breaking his agreement when he bought the ticket, and if he was not asked to leave, then the promoters were being very nice to him and saying "go back to your place in the nosebleeds".
It's a privately owned building, so usually, if someone wants to get you gone, and they are running the place, you will be gone, nothing illegal about kicking someone out.