Chomsky had stated earlier that there are experts to read who cover such things. The kid kept asking variations of the same question. If I were Chomsky I would have been done after a couple of responses.
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.
What's your point in saying so? I would guess that Chomsky could care less about winning an Internet "argument" with some random dude. From his point of view, it's entirely reasonably to say "go read the literature and come back when you're more informed". If the other party doesn't want to do that, they have no moral claim to Chomsky's continued participation in the discussion.