He was trying to cover his own ass. The QA team should be blame too when something is broken in the production.
Pretend that you were not aware of the QA manager's email.Email your manager about the cause of the incident and bring up your concerns: if the QA team doesn't have a good testing coverage, things like this could happen again. Propose test cases review meeting with both your manager and the QA manager attending. This is a chance for your boss to check out the QA manager himself.
Your boss is at your side because someone blames his team it makes him look bad. You need to give your manager something solid to fight back.
Overall, if you don't trust the QA team and don't want to deal with them, you need to have your own testing code.
