I think you are misunderstanding. The post you are replying to clearly said they were reviewing output code before checking it in. The fact that we don't understand how the models work is irrelevant (we don't understand how the human brain works, either) - all we need to understand is how the output works.

I had a conversation with ChatGPT where I asked it to write me a piece of code. After it wrote the code, I reviewed it, and I told ChatGPT that it had a subtle bug. ChatGPT then fixed the bug itself, and wrote an English description about how the fix it added would prevent the bug.