"Unwarranted conclusions" means coming to a judgment or belief without enough evidence or justification. It's like making a guess or assumption without having enough information to support it. Full definition
The statement «last winter was cold where I live, hence I doubt global warming» is just an extreme example of drawing unwarranted conclusions from one uninformative data point. (realclimate.org)
However, I believe that Bogle came to an entirely unwarranted conclusion about this... (arichlife.passionsaving.com)
Chapter 2, on the «Roots of the Crisis,» surveys Western history and draws unwarranted conclusions concerning the relationship between metaphysical realism and the late medieval nominalism of William of Ockham. (firstthings.com)