Now that I've read the paper, the optical idea is pretty simple. They put a tiny lens in front of their pattern (say, on a product). The lens acts like the objective of a microscope. It focuses light from the code as parallel rays. (I suppose that's actually un-focusing the light!). When you point a camera at this, even from a large distance, it acts like the eyepiece of a microscope and, when focused at infinity, focuses an image of the bokode onto the camera's sensor.
This very long microscope is very sensitive to angle. A focused image is insenstive to distance though the size of the image will vary with distance.