If it's a retro-reflector, how's all the footage on the site showing that images are appearing outside the retroreflective area and on top of the tracking markers?
It appears that they have two boards: a flat board where the images are limited to the reflective area, and a bent board (which has a flap that lifts up at an angle) so that you can get an actual 3d visual...for 3 out of 4 players (the image is still limited to the reflective area, but the reflective area is now 3d instead of just a flat plane).
I suppose there's a chance that something that is within the confines of the play mat from the player's perspective could appear outside of it to a theoretical outside observer, so they made their marketing reels have stuff appearing outside of the retroreflective mat.