What about in the case of (and I've been the player on the turn player side) if you NoC a "monster" and it is a spell or trap while your opponent had 2 cards in hand, a sangan and a flip effect? Also note that MoF had brought the NoC back to the hand before the spell was 'accidentally' placed in the monster zone, on the turn before.
I see this as a game loss, as the player could have wanted to know what action the opponent was to take, use the NoC or attack the F/D monster. But when this happened, the judge ruled a warning and let the player replace the card with Sangan. It was in a SJC also.
Point is, the judge has to use many factors to make a decision on what penalty to assign. The players history might play as a factor also. And, sometimes, you will disagree with the decision made or not understand why. But you just have to accept it.