There are several ways to do depth mapping with just a single camera. Structure from Motion, and Multiple View Geometry are a couple. Of course, more sensors

There are several ways to do depth mapping with just a single camera. Structure from Motion, and Multiple View Geometry are a couple. Of course, more sensors will usually provide better data. I imagine there are plenty of situation where this app with behave poorly (e.g. low light, scenes with little texture), they just don't show it in the demo.