Gritty seafood explained

I ordered a snack this afternoon which was the shrimp popcorn. While eating I noted a gritty sensation to the shrimp. Could somebody explain this grittiness if you had this meal before? However 4hrs later I experienced abdominal cramps with diarrhea. It then clicked. The shrimp was either old or not washed appropriately ( understand the water shortage in Cape Town). Please adhere to hygiene standards. And please keep the cold chain intact. I’d definitely not return.