I don't think this is true. Think about it - if you're blocking connections for remote control you need to block EVERYTHING on that connection frequency.
If television broadcasters can get a connection to send their video signal then a means of connection exists. Or if the average person at the event can get an internet connection via their phone... A drone can get a connection through that method too.
Maybe they block a common set of radio frequencies used by radio controlled devices or something. But they aren't blocking everything and can't or they wouldn't be able to run the event. A drone can be controlled from many different means, if an internet connection to your phone exists then it also exists for a drone equipped to be controlled in that way.
