You're only committing a "appeal to authority" fallacy if you contend that something is true because the person saying it is "an authority." Pointing out that someone is clueless on a topic and suggesting they read the literature and gain some baseline knowledge is not the same thing at all.

As to whether it is, as someone said above, "simply ceasing to argue" one can rightly say "so what?" None of us owe some random person on the Internet our participation in their argument. Time is valuable and it's entirely reasonable to check out of an argument or discussion and say "here, go read these books" if you don't stand to gain anything from continuing the dialog.