Yeah my read on this is that Feynman enjoys being kind of a know-it-all prick, but he caught himself here for the sake of the interview.

His first instinct was to be a dick about it, then he sort of softly walked that back using an excuse about it being a long explanation. In the end, he gave a good answer, he just had to first pretend that it was a pain because of how smart he is and how much he understands.