That line of thinking usually pairs with 'If there isn't a law against it then it must be Ok'. So the world becomes burdened with complex rules and laws to prevent people having to live in a hellscape of Jerks.
Some people are allergic to rice. Some people are on medically prescribed diets. Maybe there's an obscure religion that forbids eating rice. Some people just don't like rice. Are they all jerks too?
That restaurant wouldn't be my preference, but if I did have to be there for an important reason, I certainly wouldn't be bullied into eating something I didn't want to eat. I'm generally strict about wasting food, but in that situation I wouldn't feel even slightly guilty about it.
If they can accommodate your request, and they typically will, you’re golden. If not, you may need to patronize a different business. It is, after all, a reciprocal relationship. If your basic needs aren’t met, and they have a stiff policy on substitution - then yes, you are a jerk for ignoring them.
The actual controversy here is that the folks in the story clearly thought they were cheating the system, and people are responding without questioning that, and some people are questioning that.
Unless you're going to call the entire story fake, then yes we have enough information.