I would think they (breeders)were culling so as not not to reproduce it, just like the mom of that pup was doing. In nature that dog would have died, so be it.
You bred these pups, so who would ya point the finger at, you didn't test for it, neither did the guys in that dogs ped and here is why!
Testing for this has just recently become available, Kim from Double Barrel has posted a huge amount of info on her site. As recently as last year or so, there was no testing.
So when it happened you culled, other dogs could carry the gene with no sign and unless they were bred to another dog with the recessive, you would never know. It takes great amounts of samples for tests that work to be developed, and when your culling so it dont replicate, your killing the test material, it is a CATCH 22
So dont be down on yourself or anyone else, we learn and move forward!