A pizza is an open sandwich

No, pizza is a toast per Cube Rule - https://cuberule.com/

Toast is an open sandwich, unless it has no topping, in which case it is just bread. Also their definition of cake as having multiple layers makes no sense, and would rule out most actual cakes.

If you take a closer look at the examples again, you’ll see that nothing makes sense. That’s the joke.

(Steak is definitely a salad, though.)

What if the pizza has a stuffed crust?