Apples and oranges, or chalk and cheese. Why would you say apples and potatoes?
Maybe an ESL thing? "Potatoes" are literally called "earth apples" in some languages (e.g. pommes de terre in French; Erdäpfel in some German dialects.)
I read it as trying to indicate that it's even more different than apples and oranges.
Not sure it succeeds in that, but I think that's the intent.
I came to appreciate typos, slightly ungrammatical sentences, and creative plays on common phrases. They are completely absent in LLM output without a specialized prompt (and they seem to struggle to make believable language mistakes even when prompted), so they can serve as a signal when judging whether the text I'm reading was written by a human.
As an aside, I observed my stance on proper English use changing in real time over the past 2-3 years. I used to be proud of writing clinically correct prose, and found mistakes in grammar and vocabulary grating. Now, I kind of welcome them and have stopped caring at all about committing such language crimes. I used to cringe when someone didn't capitalize the first words in their sentences - not anymore. I think we're years away from LLMs convincingly faking human-like mistakes (since all the work currently goes into avoiding them), so it's going to remain a useful signal for a while.