I wonder if their move selection algorithm takes into account the "surprise" factor: given two moves that are almost equal in strength when analyzed to a depth of N, chose the one that looks worst at N-1. That is, if all else is equal, assume that you can search deeper than your human opponent, and lay traps accordingly.
Besides trap-laying, there's also a second useful "surprise" factor: your opponent is likely to have spent time on your clock to read out follow-ups to your most likely move. By throwing in an unlikely (but still good!) move you're forcing them to expend time on their clock to re-think their follow-ups.
That's interesting. And a sign of truly understanding what a human would think.
Btw. There's a concept in Go called "overplaying". That means selecting a move that isn't objectively the best you could come up with, but that is most confusing, considering the level of the opponent. It's generally thought of as a bad practice, and if you misestimated the level of your opponent, she can punish you by exploiting the fact you didn't play your best move.
I don't know about surprise, the the AKA stream was pretty shocked when AlphaGo was playing aggressively from the 5th line/column from the right early in the game. Apparently going in on the 3rd is already very risky and the 4th is almost never done.
