I think responding to the question with "Israel has a right to exist as a state with equal rights" is the best way he could have phrased it. I know the preferred way for those on the left is "no state has a right to exist," but that's not a sentiment that's going to resonate with liberals, and many would see it as "scary radical wants to burn it all down."

His answer is a clever way of proposing a one-state solution without freaking people out.