Our public school had fish on Fridays (60s/70s) and it was not even a predominant Catholic town. In fact, the Catholic church was in the next town 10 miles away in a different district.
It’s a nice commemoration of what Jesus did for us, IMO.
I went to a Southern Baptist college, and WE had fish on Fridays. We crabbed (bad pun) about it to the lady who ran the cafeteria. She explained that we were being sensitive to our Catholic “friends” who attended our school. So we went to Der Wienerschnitzel or McDonald’s for lunch, and out for Mexican food for dinner. If you couldn’t afford to go, several would always chip in for your food. We told the cafeteria lady that WE were being sensitive to our Southern Baptist brethrens’ need for tacos and beef enchiladas.