It looks like there's some debate whether the people with Allen that night really were cheapskates/ingrates, or if it was just a misunderstanding, so I'll forego comment on this particular situation.
However, I think some people misunderstand the concept of "casino comp etiquette", which has pretty much existed for decades.
Just because you invite someone to dine with you "on your comp" doesn't mean you are committing to give them a free meal. There's still the matter of the tip (comp can't be used for that), and the matter of any overages which occur.
Casino players like Allen often get mailed or awarded medium-sized or large, one-time-use comps, which can only be used for food and beverage. At that point, Allen has two choices:
1) Use it for himself and let the rest go to waste
-or-
2) Invite others to share in the food in order to use up the comp
This is VERY DIFFERENT than "taking someone out to dinner" or offering to pick up the tab.
This is saying, "I have too much food credit to use on myself, would you like to come and use the remainder I can't?"
It's still very generous, because Allen EARNED these comps through his casino play. By sharing his comp with you, he's giving you something for free that you didn't earn.
In appreciation for doing that, the person/persons eating the comp meal is expected to cover the tip and any small overage which occurs.
I'm not talking about covering an overage where the comp is $50 and the bill is $450. I'm talking about situations like this, where the comp is $60 and the meal is $64.
The basic rule of thumb: If the bill comes out fairly close to the value of the comp, the guy providing the comp should walk out paying zero cash out of pocket.
Why? Because he's already contributed MORE THAN ENOUGH by paying for almost the entire meal with his comp.
Many people would call me a cheapskate, and yet I always make sure to pay for the full tip AND any overage when someone takes me out for a comp meal. I'm not just virtue signaling. I went out to several meals on others' comps over the past 7 weeks, and I immediately volunteered to pay the full tip each time. Similarly, when a friend went with me on my comps, he offered to pay the tip, and I didn't argue, and let him do it. That's the way it works.
If you are so entitled that you think Allen's "invite" means that he's going to cover overages and the tip out of his pocket because you graced him with your presence, even though you're eating with HIS comp, then you either don't understand how all of this works, or you're an ingrate.