Learn English – More professional way of saying Correcting a Mistake

The first word that came to mind was tentative (unsure; uncertain; not definite or positive; hesitant).

After reading more carefully, I think a better word to use would be proposed (to put before oneself as something to be done; design; intend), as you have both put this collaboration before yourselves as something to be done, but it is still subject to confirmation.

Would you like to tell me more about your ideas for our proposed collaboration?

I think you are dealing with a real bad case of confirmation bias.

Confirmation bias, also called confirmatory bias or myside bias, is the tendency to search for, interpret, favor, and recall information in a way that confirms one's preexisting beliefs or hypotheses, while giving disproportionately less consideration to alternative possibilities.

That being said this person is clearly unqualified to make OR deny a diagnosis.

References:
https://en.wikipedia.org/wiki/Confirmation_bias
https://en.wikipedia.org/wiki/List_of_cognitive_biases