While that was bad enough, I really got irritated that the DM did nothing to stop them, or say anything to them on the SI. I guess the DM was hoping for a tip from them, but I think he did not know tipping is not customary in their culture, so he got the reward he deserved for that dive.
It may be instead that what he was hoping for was to keep his job. I would bet that many an operator around the world has a "don't piss off the customers" policy for their DMs.