Did Lee Sedol have a reasonable idea of AlphaGo's recent strength? To put it more harshly, did DeepMind misrepresent the true strength of the program?
I find it very hard to find information about this online.
I find it very hard to find information about this online.
So far, they have tested a previous iteration of the program against a much lower level professional, as well as all of the other Go engines they could test it against. It easily defeated all other Go AIs, but no previous Go AI has been able to compete at a professional level. It also defeated Fan Hui, the lower level professional, though it made several mistakes and lost a couple of the informal games (with lower time limits) it played against.
Since then, they've had several months to tweak it, and then let it train against itself some more. The thing is, to really determine its strength, you need to have it play serious games against professional players. So there really was no good way for them to determine its strength without playing these games. It's possible that it only would have improved a little since it's games with Fan Hui; in that case, the match with Lee Sedol may have been easy for him. However, it appears that it has improved substantially.
On the other hand: Knowing what makes some problems much easier for humans than for computers can have direct value on Google's business. Go was a hot candidate for a game with this property.
How much publicity has Google received for $1 million? (Much less than that actually, since they won)