I have worked on NLP systems for decades, the usual pattern is converting a request into structured data, and sanity checking the structured extracted data. If you ordered a pizza with rocks on it, the ‘toppings’ filed would be checked against a datastore of available toppings.
Makes sense, but then where would the fun be in putting in ridiculous orders, and I wonder how the Taco Bell system is responding when people order completely off-menu items like pizzas ?