Building the wall down to attack the bottom right corner isn't something outrageous, not to those at the level of Sedol. AlphaGo definitely played amazing, as the game was very technical in term of fighting. But the "flow" (chase out weak group then invade a corner) is a fairly common situation. I don't think it's a matter of AlphaGo seeing strategy further than Sedol. It might have had much deeper calculation and reading than Sedol - as showed in deflecting the attachment in lower right - but that's a bit of a different story.
