[friend_and_foe]

I don't think the goal here is code review. They're trying to gauge a few things: 1) are you competent? 2) are you coasting or genuinely contributing? 3) are you actually dedicated to improving the product or more concerned with office politics and inserting your ideology?

A quick interview and a little demonstration of contribution can help assess these things significantly, you don't have to understand the codebase that much to do it.