Comment by quadrifoliate

I think there is a simple, unambiguous way to describe this, which is to use the passive voice or an explicit subject with the past tense to clarify that you didn't do the opting in.

Saying "we were disappointed to be opted in to training by default" clarifies the point you're trying to make, which is that the toggle (whatever it may be called) was set to training by someone else, not you.

Actually in your case you'd say "...after being disappointed that the Pro tier opted us in to training on prompts by default", which gives an explicit subject ("the [Mistral] Pro tier"). No one will confuse that with the opposite "the Pro tier opted us out of training on prompts by default".