That would be about right considering Ke Jie is 8-2 vs Lee Sedol and assuming Lee wins one. That assumes that we are seeing AlphaGo's strongest game and not its "just past the current opponent" game. If Lee doesn't win any then it is very difficult to estimate AlphaGo's strength from the games. If Lee wins one game then a 50-50 AlphaGo vs Ke Jie would be expected.