It is indeed a fact that OpenAI's Terms of Use do state that you can't use their service to develop competing models: Section 2.c.iii -
https://openai.com/policies/terms-of-useNow of course, the terms are not the law (so don't govern the use of the generated data by any third party), they are an agreement between two parties. If you did click "agree" then that's a binding agreement and there could be legal/contractual repercussions (some of which are outlined in the terms).