Most people have no idea what's in the foods they eat. Why do you think fast foods are so popular?
Shrimp farming didn't begin to scale up until the mid 1980's or so and has grown very large since then. So your grandfather didn't have much opportunity to eat "those damn farm raises shrimp".
When I would go visit my father in Ft. Walton Bch. Fl I would get shrimp that were 2 hours off the boat. They were excellent. Much better than the shrimp I can get in the local stores here in Texas unless they have fresh gulf shrimp, which is a hot or miss situation.