In that part of the video, we see an exchange like the following between Chomsky and one of the members of the audience. (I am copying this from the Appendix in the Ludlow book (p. 187).)

***
Audience: ...what kind of empirical evidence would count in adjudicating between those.

NC: ... What is the empirical evidence that bears on whether anaphora is on one or the other side of the border of the language faculty? Well, part of the empirical evidence -- in my mind at least -- turns on whether in fact there's a single cycle derivational process that goes by, what I call phases, stepwise. That's an empirical question but all kinds of things bear on it coming from everywhere. And once that empirical question is sharpened, you can ask whether the global property of anaphora is inside or outside.
***

That's an empirical question. Perhaps it is. But how can we go about answering it on the basis of rigorous experiments? My book proposes what I consider to be the first step toward doing that.