I believe there are 2d elements there. The blurb on the video says:
Introducing a groundbreaking technique that seamlessly merges computer-generated and hand-drawn animation techniques, first-time director John Kahrs takes the art of animation in a bold new direction with the Oscar®-nominated short, "Paperman." Using a minimalist black-and-white style, the short follows the story of a lonely young man in mid-century New York City, whose destiny takes an unexpected turn after a chance meeting with a beautiful woman on his morning commute. Convinced the girl of his dreams is gone forever, he gets a second chance when he spots her in a skyscraper window across the avenue from his office. With only his heart, imagination and a stack of papers to get her attention, his efforts are no match for what the fates have in store for him. Created by a small, innovative team working at Walt Disney Animation Studios, "Paperman" pushes the animation medium in an exciting new direction.
Either way, some impressive stuff. Puts the efforts of Anime producers to shame, as it's really seamless. Of course, Disney has always been good at the technical stuff. It's a great short, but I'd be interested in seeing if they can use the technique to make a great movie. Time will tell...