“Honestly, if I had a restaurant I’d do that to just about anyone with some fake “allergy” to gluten or nuts.”
Nuts - very often people are referring to peanuts which are not nuts, but legumes or cashews which, also, are not nuts, but seeds.
Gluten - 2 issues
Celiac - some are born that way, some develop it. They cannot afford to ingest any gluten - even cross-contamination has to be avoided, ie you cannot even give them something on a plate which has recently had gluten containing foods on it. The plate would have to be properly washed fist. Failure to do so could result in severe intestinal bleeding for several days afterwards.
Gluten intolerance (not allergy) - this occurs in various degrees and is more common nowadays as a result of the hybridisation of wheat which changes the nature of the gluten. Develops over time. Some people can tolerate small amounts so long as it is not a daily thing. For instance, I can tolerate a small amount in a gravy if I were eating out, but I would not order a sandwich.
All contribute to kidney stones in a big way!