I think the "you" in the quote is referring to the programmer of the PR, not the reviewer. I agree that it's probably unrealistic to expect reviewers to understand every line of code in a PR. That's why it's crucial that the programmers of said PRs themselves understand every line of code. I'll go one step further:
If you submit a PR and you yourself can not personally vouch for every line of code as a professional…then you are not a professional. You are a hack.
That is why these code generation tools are so dangerous. Sure, it's theoretically possible that a programmer can rely on them for offering suggestions of new code and then "write" that code for a PR such that full human understanding is maintained and true craft is preserved. The reality is, that's not what's happening. At all. And it's a full-blown crisis.
If you submit a PR and you yourself can not personally vouch for every line of code as a professional…then you are not a professional. You are a hack.
That is why these code generation tools are so dangerous. Sure, it's theoretically possible that a programmer can rely on them for offering suggestions of new code and then "write" that code for a PR such that full human understanding is maintained and true craft is preserved. The reality is, that's not what's happening. At all. And it's a full-blown crisis.