Most participants in this debate are far too preoccupied with the shape or structure of the sandwich, to the point of neglecting what a sandwich is all about. It's simple. A sandwich is when you use bread as a handheld base for prepared foods that would otherwise be too messy to eat with your fingers. A tortilla is a flat bread, ergo handheld burritos and soft tacos are sandwiches.
"Then why isn't pizza an open-faced sandwich?" Because pizza has a crust, not bread. When you take raw dough and bake it along with its toppings or fillings, it may be a pie or a pastry or a pizza or a casserole or some other category I don't care to quibble over. It's not a sandwich.
Obviously there are many sub-categories of sandwiches. A dish isn't necessarily excluded from being a sandwich just because it's also another type of food.
Would a tostada then be a floppy cracker fried crisp?
No, crackers are a type of bread. Tostadas are cracker versions of tortillas. Corn tortillas are whole grain flat breads.
Pupusas and tamales are like his pizza example where the masa dough is cooked with its fillings. But those are both types of dumplings, which would make pizza an open-faced dumpling 🤔