Im not sure I agree with that. There is no bread involved, and possibly worse for team sandwich, there is only one continuous wrapper. I don’t care what the tax man says that shit ain’t a sandwich. If anything it’s a sort of calzone.
We label foods based upon the number of carb sides.
Open face sandwiches are not a thing. A sandwich requires two non-contiguous opposed bread layers, otherwise it isn't a sandwich. It's a pie. A bottom carb layer with a top layer of substance. Pizza, pie, "open face sandwiches", and French parfait are all pies.
Now, by having only one contiguous bread, but covering three sides, that would put tacos, hotdogs, Philly cheese steaks, and subs all in their own category (arguably a misshapen pie, but that's a deeper debate).
It's weird in my area. We say toast and jam but call meat and cheese on toast a sandwich. I guess I'm my mind, more than once topping kind of makes it a sandwich, however ... Eggs and cheese on toast but Neuchatel and jam on toast.