Multitouch, Microsoft Surface and NUI Ideas.
My guess is they are doing a contact size/shape comparison or something fairly simple like that. It's probably fine when they only have 3 different lenses in a demo, but it might be tough to make it reliable when there are dozens.
The two lenses seem pretty similar in size and shape. That may just be youtube's low resolution though...Do these demos ever make you think of 3 card monte. Follow the card. Follow the card...
It probably is fixed for demo purposes, but they could have had invisible infared tags. Same byte tags, but the sticker is transparent except for infrared reflective paint dots.
OR they could be detecting the luminance of the object