Mixed pizza

The last Sunday of my parents visit to Washington, we went to eat in a small pizzeria tucked behind a shopping center. I am no fan of pizza but my dad is and he wanted to get a taste of "American pizza". For comparison I guess.
We're waiting for our order to come when I see one guy walking in the place. He gets to the register and I hear "$19.90" . He pays, takes a large box which is just next to the cash register and walks out. The whole scene has lasted maybe 30 seconds.
As soon as he has walked out, another guy comes by and I anticipate the same scene except that we all hear a small shout from behind the counter and I see the cashier jumping out and running after the first guy that left. They mixed up the orders. He has left with the order of the second guy who is standing there, waiting for his pizza to come back.
It eventually does. Apparently the cashier caught the car of the first costumer as he exited the parking lot. He is holding what he thought was his, handing it back over the counter and grabbing the other box. The cashier apologizes and he smiles saying that "no harm done" but I see him stopping on the way out and opening the pizza box to check it content.