According to OpenAI, they only harvest data coming from ChatGPT (their app), but not from third parties using the OpenAI API.

> How we use your data. Your data is your data. As of March 1, 2023, data sent to the OpenAI API will not be used to train or improve OpenAI models (unless you explicitly opt in).

> Note that this data policy does not apply to OpenAI's non-API consumer services like ChatGPT or DALL·E Labs.

https://platform.openai.com/docs/models/how-we-use-your-data