Norovirus is typically a virus that is associated with Human feces, fecal contaminated waters, and fecal contaminated produce
Foods that are typicall affected are Ready to eat foods such as salads, sandwiches , baked potatoes, oysters fruits and vegetables
either the water was contaminated by sewage, or some worker serving them didn't endeavor practices using the commode that are learned at an early age, and did not wash their hands, and touched food, or there was cross contamination somewhere in the chain of events...
Am not a scientist ,but just took a class on food safety..I'll check my notes again but from what I remember boiling , high temp, helps nothing if a product is infected with a virus
Aim for Sucess, not perfection
Good Country, This America