This can become an issue for religious vegetarians, too. In India when you say that something is vegetarian it contains no gelatin or animal fat or anything like that. Vegetarian food is prepared separately.

Orthodox Hindus who move to the West often struggle with this. Even ice cream (marked as vegetarian) sometimes has gelatin. You can ask for vegan food, which is an approximation, but "no milk" is the antithesis of many Indian diets :)

I know such families who basically never eat out ever, and prepare things from scratch at home. Though they usually are more lax on allowing the kids to eat pseudo-vegetarian food.