People who fly Stampes/Moths etc tend to be fairly knowledgeable and experienced pilots.
Had either of our two 30,000hr chaps been that concerned , then surely the best way of dealing with this would've been to walk over and enquire if the pilot in question was aware of what he was doing.
He may well have been a lesser experienced guy who could have benefitted from the OP's superior knowledge .
Or he may have been flying Moths/Stampes for as many years as his observers have been flying.
But they can't answer that ; because instead of making a positive input , one of them decided to put it onto a forum instead !