AlphaGo was well below Sedol's level when it played the European champion in October. It must have been a bit uncertain how quickly they could improve it.
How clear is this? If this just comes from professional humans saying "I would have played differently, and I could have beaten Fan Hui by more points" - well, we've seen that humans aren't necessarily very good at judging AG's moves, and we know AG doesn't care how much it wins by.
http://www.nature.com/nature/journal/v529/n7587/fig_tab/natu...