I googled to see if he had any published thoughts and found this:

"(The ending) is specifically designed to be ambiguous. What's funny and interesting to me — and not to sound too cocky about it, but I really do think it worked — is everybody talks about the specifics of what's happening in that scene. And to me, the specifics don't matter that much. And I'll explain.

"What is happening, what is going to happen, all that is just fun to talk about. But what's important to me is that these two people are on the same page and are seeing the same thing. There's several interpretations of where they're at. And that's great. But as long as they're seeing the same thing I think there is a resolution and the possibility of hope in the film."