Comment by semi-extrinsic

The idea is that they embedded this when it was a new model, as part of the hype before GPT-4. The fake-it-till-you-make-it hope was that GPT-4 would be so good it could actually play chess. Then it turned out GPT-4 sucked at chess as well, and OpenAI quietly dropped any mention of chess. But it would be too suspicious to remove a well-documented feature from the old model, so it's left there and can be chalked up as a random event.