I don't understand why he (or anyone) thinks it's OK to say, cheat in an algorithmic interview, but that if you were somehow able to have an LLM secretly feed you optimal answers for any other part of the interview it's "wrong".

Why is it not OK to cheat on a system design interview? Why is it not OK to completely make up a story to make you look amazing when they ask about your background?

In the article he thinks companies should review past work and ask interviewees about that instead, but what would he say if there was an app for cheating that way?