Any published work is copyrighted by default. Are you aware of Chomsky making any effort to keep his books out of people's hands? Has he sued anyone for copying or distributing his books?
But it is easy enough to declaim the restriction to copying if one wishes CC-SA, CopyLeft, CC0¹, PD etc.. Chomsky is likely contractual obligated, at least in part, if he holds a tenured professorship and may not be able to do this without leaving that post.
If he's contractually bound then I think it would be fair to say that he is railing against the restrictions imposed upon him rather than being hypocritical.
Of course, this is all speculation until someone either gets a response out of him on the issue, or he starts chasing down "pirates".
