Yeah... I'm not sure what that is. They also conflate mA and mAh a few times. It's kind of confusing.
I think that they are using the weight of lithium metal rather than the actual battery. That's the only thing that makes sense, as the specific energy of PURE LITHIUM is barely above that 10.5 Wh/g figure. The 10.5 must come from the energy drop to sulfur intercalation, which is at .4v. The 8.5 Wh/g figure comes from the reversable voltage range. It's either that or their numbers are off by 100x.