The difference being you don't insert money at the start to play. So you are gambling nothing. And you are playing against other players, not the house, so every player has as much chance to win as any other player, it's not like blizzard is skimming results off the top.
So...err no... in fact it is fundamentally nothing like a casino slot machine. If you had said it is heavily based on RNG, like pretty much every single mode of hearthstone gameplay, then yes. But you didn't say that.