This is largely my take as well. When I review code, I am checking for correctness. If I find something is not correct, that's a bug (or a bug waiting to happen). If I can't understand whether or not something is correct, that's a problem. If I don't know what the correct behavior should be, that's a problem.

Though I do think there is value in the original post. Re-framing is a powerful creative tool when you hit a mental dead end. And the responses let people share the other benefits that change management can bring.

Personally, I would tell you that whatever understanding you gain may still have bugs. Unless your understanding is as complete as a formal treatment of the code, then there may still be bugs in the code due to shared misunderstandings between author and reviewer. The biggest one is both having an incomplete understanding of what a library function does.

So while there may be some overlap, particularly if each person has full understanding of the code's dependencies, in the general case, understanding code and finding bugs are quite different aims.