But there is evidence, the blog post says: "While unlikely, we cannot rule out that de-identified data derived from their usage of our products helped improve our models ."

In other words, yes, they had been using ChatGPT, and yes, ChatGPT could very well have trained on their data. Now that there is evidence, we need an investigation: yes or no, was it the case?

But the evidence is in the hand of the potential culprit. That's why allegations can be enough to force confiscation and intrusion to get evidence in safe hands before it is destroyed by the accused party.

That is backwards. It is the responsibility of a researcher to do a thorough literature review and conscientiously avoid plagiarism or claiming false novelty.

Nobody except OpenAI knows whether or not OpenAI trained on their data. So the burden remains on OpenAI here.