The system could fairly accurately be described as echolocation, just like bats use: it measures the time it takes for a sound to produce an echo at different points in the room. Essentially, what they've come up with is an array of microphones and an algorithm that picks up both the original source and its echoes. Our ears can't hear the tiny lags that make up the echoes in most sounds, but bats can, and so can this system.
From a single sound, they can reconstruct a room to within a few millimeters--provided the room isn't too complicated, at least for now. The system outputs a 3-D map, which until now could only be made with visual tools like LIDAR.