I disagree somewhat. It should not be possible for a plane to leave the factory without completing all QC checks. People are fallible, so a robust process is critical, and designing/confirming a robust QC process is a QA responsibility.

How do we know that it was just 'someone was supposed to be checking the bolts before the plane left the facility and they didn't'. Because I'm not sure it's actually been fully revealed where the problem was. And despite the production issues, I'm of the opinion that the door-plug design should have been fail safe like the other doors where just pressure prevents them from being opened during flight. And another thing, passing the buck to QA doesn't let engineering off the hook since QC in this setting is a part of the engineering!