Right now, it looks like they're more fishing for how you'd handle new situations than for qualifications and all that stuff.
Got to disagree with the "What you know now is utterly useless to him" comment. Obviously it would seem to be of *some* use (otherwise why the 3rd interview?) But, IMO, a 3rd interview is more trying to find the intangibles of a "fit" rather than anything else. Gawd knows, I've *known* some people whose only goal in applying for a job was to be able to put a line on their resume and move on after getting "X" years "experience" (in the case I'm thinking of, I think he quit after a year, which is of course a quite unsatisfactory result of a job search/job offer/job acceptance/employment process from the employer's perspective).