It seems that in this case OpenAI are suggesting that the researchers whose work they scooped were using OpenAI models with an account setting that allowed OpenAI to train on anonymized prompts.

It seems that Buckmaster and Levant (who is an Anthropic employee) were rather naive in the amount of trust they had in OpenAI, with Buckmaster going so far as to contact OpenAI's Sébastien Bubeck to discuss what they were working on and clarify that contrary to rumor this was a private collab.