We don't know what to make of it, except that it really looks like a rear camera, not just a sticker, and with something like an LED flash to boot. In the video a father seemingly takes a snapshot, or is aligning somehow an image of his son's room, to print him the dinosaur wallpaper he asks for.
Either the video has been created before HP made the final decision what to include in the TouchPad, using another prototype, since rear camera is not one of the features listed, or it will be included, after all, between now and June, when the HP TouchPad hits the market.
The scene, where the webOS tablet sports a rear camera, and some sort of AR app, starts at about 2:25 in the video below.
source: HP via PreCentral