I am no expert but my take is that you probably can’t know. However, if there was an AI that truly played HS for you (and I mean truly playing, not roping and pressing hero power like bots do), everyone would know this exists. Even if an AI was playing the game right now it would just be in 1 account; so if most people don’t know about it, chances are you have never played against an AI.
But again, I have no idea about AIs or computer science so that’s just a guess.