Sad. This stuff happens more often then we would like to think about. This is what happens when you employ goyim in Jewish food establishments. Additionally usually the employees aren’t that intelligent so even if you tell them NOT to do something they will likely forget and do it again. Remember to them it seems like no big deal its “only” a sandwich in an oven my gosh what’s the big deal?!
I am jealous of Jews that never purchased anything from a bakery or takeout in their lives.