That’s a big part of the difference. Cats in the old world are probably fine since everything there has evolved alongside them. But the native species in the Americas haven’t had housecats to worry about until relatively recently in evolutionary terms.
The door to the back is a portal to the elemental plane of pizza. Employees dip into the back to slay a pizza elemental and harvest its crust whenever they run out of dipping sticks.
I think the joke is that nobody ever actually enters LC. They just order from there. So there would be no way of knowing if it was actually secretly an entrance to the backrooms