If he hasn't observed at least a dozen such children trying to learn language for a dozen years then he doesn't even know what are the things he doesn't know.

And guess what, I watched your video and even Chomsky admits that he only heard about few cases of feral children of which the one he talked about in detail means little because the girl was severely mistreated by parents in addition to growing up in isolation. And then he talked some more about other people inventing their own languages, but not living in complete social isolation.