The restaurant was not closed for overcharging the tourists, it was closed for health violations. No doubt the restaurant behaved badly but one of the things of the couple ordered was 180 euro bottle of champagne.
As to the person who was charged 20 euro for a sandwich, you were certainly under no obligation to purchase this sandwich unless you ate it before asking the price. Mobile food carts near tourists sights always sell items at a huge markup. The buyer needs to accept some amount of responsibility.