The casino may be open to the public but it is a privately owned entity. They would require very little reason, in the way of justification, for removing someone from the premises. So you sue? BFD. What were your damages? The admission fee? Just because you sue and win doesn't mean you're automatically awarded a big payday.
Even if you are awarded a big payday, collecting is a whole 'nother matter.
You can claim all sorts of damages and a jury could also award punitive damages.
Sure you could sue, but what for? Civil law is some of the most boring stuff there is, you could die under all that paper and your case would never come to trial. This is where as a business owner you would have to do an "actuarial analysis" - does it cost me more to offer some sort of minor settlement or more to defend this thing? Like saying here's 10 grand, now go away and before you do sign this statement that says you'll never try to enter another venue where I'm holding an event. The courts are full of these law suites. I don't know either of these people, but really, I kinda doubt that either of them are seriously considering this as even a slight possibility. Just sounds like they're both pissed off