They're fudging the numbers and not counting sugar alcohols and glycerin. But many people do metabolize these and find they cause an insulin response, so the net carb count for them is much higher.
See here for more info:
http://www.phlaunt.com/lowcarb/19059967.phpDo sugar alcohols give you bad gas and diarrhea? If so, congratulations! You can freely eat foods with sugar alcohols knowing that your body doesn't metabolize them, because the bacteria in your gut are clearly feasting on them. Just be sure to bring a spare pair of pants along with you (speaking of "fudging the numbers"). Sugar alcohols are like Olestra or Alli. Not worth the risk, in my opinion.
Of course, YMMV, as always.