How does that make the theory of evolution different from anything else? Anything that humans accept as "fact" could be wrong--we could all be brains in a vat dreaming everything, for example.
For practical purposes, though, most people accept some things as pretty well proven to be true, rely on them and call them "facts," for lack of a better word. We couldn't function otherwise.
For most people who don't have an emotional need to believe otherwise, evolution through natural selection seems the most reasonable explanation for why animals are the way they are. The evidence just keeps mounting and is available for anyone to read in textbooks, websites and other written materials. At a certain point, it becomes pointless to keep pussy-footing around and not use the term "fact." I mean, some flat-earthers or hollow-earthers might disagree that it's a "fact" that the earth is round and reasonably solid, but the average person can't be expected to keep an open mind on those points forever.