My favorite Bonker's World cartoon points out that the code review process alone does not necessarily ensure the quality of the code.
When you are living in the open, however, you as a reviewee are restrained with an extra incentive to be more careful, lest you embarrass yourself in public with silly mistakes. The reviewers have the same extra incentive to find flaws in others patches to earn their karma points. It also helps that any bug becomes shallow because the reviewers competing to find issues in your code gives any change a large enough number of eyeballs.
It is no wonder that the open source process can produce better-quality code more easily.
Unless you are working on fixing a vulnerability that is still under embargo, that is. It is even worse if the bug is in an obscure corner of the system you do not personally use very much.
You can only confide in a few of your trusted lieutenants, who all tend to think in a way similar to yourself. This greatly increases the chances of simple and silly bugs go unnoticed. And it makes you feel uneasy and stressed. You get only one chance to get this right, or the disclosure goes out. This is especially true when you thought you have everything tagged and ready, and decided to take a nap while waiting for the embargo to expire. It suddenly occurs to you that there was a corner case you missed, and you have to scramble to redo the fix.
Now that the embargo is over and the release is out, I can relax ;-)