It kind of depends, not every task are the same. you won't review a trivial change the same way as a brand new feature.

Let's take for instance the fictional case of adding a list of website to a whitelist.txt. Maybe the source file had thousands of websites to be added. Anyone could add or remove some in the middle and no one would ever know

It looks good when you review it. but there is no way to check the data integrity (at review time), you can only rely on the good faith of your coworkers.

I am not saying that's what happened but this is a good example of how anyone could sneak-in arbitrary code that pass the code review.