This is only true for the free tier. Paid Ai Studio users have strong privacy protections.
I have google workspace business standard, which comes with some pro AI features. Eg, Gemini chat clearly shows “Pro”, and says something like “chats in your organization won’t be used for training”. On AI Studio it’s not clear at all. I do have some version of paid AI services through Google, but no idea if it applies to AI studio. I did create some dummy Google cloud project which allowed me to generate api key, but afaik I still haven’t authorized any billing method.