Another anecdotal data from an arxiv preprint [0]: "After the paper was written, the author learned that the same result was also proved independently and by a different method by Ningyi Li [7]. The result is also contained in a paper [8] released by OpenAI on October 6, 2026, in which the proof strategy and specific choices of notation are identical to a preliminary version of the present paper that was uploaded to ChatGPT on September 8, 2026."

So not only did OpenAI publish a proof similar to one discussed on ChatGPT, but also there were other possible strategies to prove the result, that OpenAI didn't follow.

Also, up to my knowledge, on the free plan, OpenAI doesn't claim that they won't use the chat data for training. So this seems plausible.

[0]: https://arxiv.org/abs/2610.10072

The "coincidence" defense never works for random individuals so I won't buy it when it comes companies worth billions which will lie, cheat, and deceive to make even more billions. They've been caught lying and stealing again and again. After so many years of this I think any trust put in them is either blissful ignorance or willful misdirection.