A late follow-up. I read an article on the study, and it turns out that the difference from previous estimates (which basically all showed a decrease in antarctic ice mass) comes from an interesting place. Everyone agrees on the height change in East Antarctica. But the studies that got a net decrease assumed that the change in height was due to recently increased snowfall, in which case the extra height will have the density of snow. This new study that gets a net mass increase assumes that the change in height is actually part of a long-term mass rebound from the last minimum, and if that's true then the density profile of the Antarctic ice sheet should be roughly constant, and the extra height will have the density of ice, which is ~3x that of snow.

I think the disagreement over this shows how big our error bars are.