While I can’t speak for this small, mom-and-pop place, I can speak for the many times I’ve eaten at Wetherspoon’s in our ‘Mother Country’. Excellent food and drink, great prices, web-based ordering. This ‘customer’ of his may be a dick, but he does have a good alternative, and even the mom-and-pop owner seems to know it. I just feel sorry for Wetherspoon’s, if they have to deal with this loser, although they probably can blacklist him, if needed (due to their web ordering system).
I have friends who work/have worked in restaurant industry. They say customers are 95/5 good/terrible. The second group are only there for a free meal. They will eat 90% of a steak, then demand to send it back. Whatever they want, they will make a fuss so the owner has to placate them to avoid upsetting the other diners.
With regard to this specific case, I have never gone to this type of restaurant where they failed to tell me up front that my wait will be X minutes. If X is too long a wait for me, I simply leave. I’m sure these people were told they had a 15 min wait. So if they sat down, they acceptted it and have nothing to complain about.