Stating a fact about an individual’s lack of knowledge isn’t “making it personal”.
Reading another Freeper’s mind to say what he does or does not know is indeed “making it personal.” If you were say “it seems to me that you don’t understand” then it would be your opinion and not “making it personal.”
It is when you are wrong and the first individual is correct. At that point, it's purely personal, the facts having been discarded.