Not surprising. When privacy is a selling point on the enterprise plan regular users, even paying ones, are the product. OpenAI had this from day one, the writing was on the wall. We all knew it so let's not act surprised now.
There's really no reason to think that enterprise plans are immune. While this analysis didn't test enterprise plans, and only focused on third party tracking, the people behind these companies have already demonstrated that they are willing to break the law to get what they want, are willing to lie to their users, willing to lie to the public, and even willing to lie to congress. Yet somehow people seem convinced that they'd never dare to lie to Random Corp LLC