The Dota 2 bot is no different than Aimbots in FPS games. The bot was able to access the api to perfectly target the exact location and instantly cast a spell, much like an Aimbot can instantly get headshots.
It's a good comparison honestly. They stripped away all the complexity of dota to this one single scenario were the things bot's are naturally going to be good at (last hitting, precise distance evaluation) matter over strategy.
