If there had been a QA process, the kill rate could not have been as high as it is, because there'd have to be at least one system configuration that's not subject to the issue.
I agree that testing can reduce the probability of having huge problems, but there are still many ways in which a QA process can fail silently, or even pass properly, without giving a good indication of what will happen in production due to data inconsistencies or environmental differences.
Ultimately we don't know if they QA'd the changes at all, if this was data corruption in production, or anything really. What we know for sure is that they didn't have a good story for rollbacks and enforced staggered rollouts.
