He speaks to a group of people that aren't gamers. or game creators. That is a very large demographic. Having someone incorrectly say game aren't art must be responded to so that the reason he is wrong are known.
Tycho is correct, it isn't really a debate. No one is going to change his mind because it is completely closed to what is art. It's the people watching the show that you are actually addressing.
Make him look like an old fool to the demographic that doesn't game. Speak to them, let them understand why a game can be art. Help the young kid who is trying to tell his parents he wants to go learn to make games that it is 'legitimate' art.