Hang on. An updraft may result in a momentary increase in g and therefore the stall speed, but thereafter, when established in the updraft, either the autopilot or the crew would be pushing the nose down in an attempt to maintain altitude. This will probably result in a speed increase. Certainly, the nose isn't going to pitch up by itself. If anything, as the speed reduces, the nose should drop by itself because the pitch trim is now way out. And this is an airbus; I don't fly them but in normal law, won't the system automatically reduce the AoA/lower the nose if a stall is approached?
A severe downdraft, on the other hand, will result in a big speed decrease if level flight was attempted. But these guys were climbing.