AI is a tool, not a solution. If someone uses it to write code they don't understand and that is flawed, that should never pass code review.
If your AI generated code passes code review without any questions asked and without any hints that it's AI generated (or AI was used in some way), then it doesnt matter that it was used.
The person submitting the code is still responsible, and the reviewer is equally responsible. You typically have tests to make sure it behaved correctly, too.
That's beside the point, we all know that one terrible engineer who is just incredibly productive and completely lacks any self-critical instincts. With LLMs this type of output becomes much more easy to produce, so what are you going to do if you're asked to review 10x the amount of code that you're reviewing right now?
Something similar happened in my job. I reported the over-engineered, completely senseless solution, after the "dev" got really angry at me about simply reviewing his code. He was gone the next week. If you have a boss, tell him when this happens. If you don't, fire him/her yourself. If the amount of complexity introduced is not worth the use cases it covers, in a business sense, then that's a review that rejects the code on that basis.
If your AI generated code passes code review without any questions asked and without any hints that it's AI generated (or AI was used in some way), then it doesnt matter that it was used.
The person submitting the code is still responsible, and the reviewer is equally responsible. You typically have tests to make sure it behaved correctly, too.