I've not read the full thread, but my boyfriend is American and we have had a few lively discussions around tinned soups being used as a sauce/base for dishes, and them calling them casseroles, so I've looked into those dishes a bit.
The green bean casserole was developed by the Campbell's soup company, I think in the 50s, because people always had cans of the soup on hand, the mushroom one. It wasn't a very popular recipe to begin with but they persisted with it! I think tater tot casserole is basically the same thing, with added tots.
He's trying to tell me how good these things are but I remain unconvinced.