I went today a family did exactly the same to us, but this was at a podium with a cashier. They looked like a normal family but were so slow I was beginning to wonder if it was a Candid Camera set-up! Then the mother wanted to add soup as a snack and the system messed up same as it did for you.
Sorry, I don't know if this has been mentioned already, but when we checked in the CM asked if we'd had an email. My wife said "no" and the CM said FP is by invitation only. My wife looked dismayed but I said we've got a FP and gave our name, and sure enough, he had it. I have a feeling it could have easily gone wrong there as BOG are not sending out confirmation emails or even giving a conf number and less forceful people might have just walked away thinking they'd done something wrong.