IMO, like stews, they should be served in a bowl along with bread for mopping up the leftover gravy.
Casseroles are old dishes; pre-industrial with a history probably going back to the post-Roman epoch or even further. Consequently, they are made very much for efficient use of whatever ingredients are available for maximum nutrition value and storage of leftovers. It is definitely not an entrant in the 'food = art' world.
BTW - What is the difference between a casserole and a stew? Stews use mostly just stock gravy and don't take that long to cook whilst casseroles have far more elaborate sauces and tend to take longer to cook because the sauce needs time to flavour the meat.
Actually, the idea of baking things together does go back quite an age for some cultures. Egyptians around the age of Christ were stewing all sorts of things together in what would appear to us today to be a sort of goulash.
However, casseroles? Not so much. Romans were using something more akin to what we think of as a bread oven, and outside of bready things the only items cooked within were items assembled within a thick flour and salt crust, later to be known as a coffin, which would be cracked open after cooking and the crust discarded. These were the predecessors to our pot pies and traditional pies, where the crust was actually eaten.
Casseroles by definition are baked, rather than stewed. Hence, a casserole would be cooked in a dish (later known as a casserole dish) and stews were cooked in a stewpot. The big difference is which method of cooking is utilized.
You could point to such British staples as the shepherd's pie as a casserole, being a dish that incldues several items and which is baked in an oven. Still, yes, it is the Americans who really perfected (or completely demolished) the grand art of casserole making, thanks to post-WWII homemakers and the introduction of the supermarket, which brought a plethora of new ingredients that were quickly adapted into middle-class life. From this era we get such monstrosities as the hot dog casserole, Spam casseroles and other gastronomicly questionable entrees, the best and most edible of which have managed to stick around to our current times (enchilada casserole and broccoli-cheese casserole amongst the more popular of these).
That being said, what American casserole makers did discover is that by layering or alternating ingredients within each casserole, they could create something of beauty with very little work. For a casserole to look like dog food indicates some sort of amalgamation of the ingredients, which means Renee might just be a crappy casserole maker. The ingredients may be tasty, but the end product's lack of viability as a culinarily alluring dish might inspire such caustic comments.
Throughout the composition of this comment, I have tried hard to conjure a single casserole in my head that might constitute the dog food comment. It would probably require extensive use of packets of brown gravy, which is another travesty.