It is true that the argument for evolution is an inference to the best explanation as most of science is and thus it does seem a bit overstating it to call it a proof which suggests deductive certainty based on undeniable premises Calling it a demonstration is at least ambiguous between calling it a proof and treating it as if you can simply observe speciation in the past when you re not there both of which would be a little misleading So I do agree that it should be reworded Demonstration is a bit strong for most scientific theories perhaps with the exception of outright laws which are fairly rare in science