The difference is there is an element of personal responsibility here. The friend is an adult who was cautious of the food to begin with. It was not a sneaky nut hidden in a sauce, its a pizza base.. which are pretty universally known for containing gluten.
Its like me wearing my shoelaces untied then suing the council when i trip over them on the footpath. I could have tied them up in 3 seconds and saved a whole lot of trouble!