I'll also bet that they knew they couldn't assure intention when things like this happen - which is why they said it has to be clearly accidental. So someone can't throw and elbow or kick someone and then use the excuse that they didn't know the other person was there and that it was all an accident.

So - if you make a move and clearly didn't know the other guy was there and there is no way to view the contact as anything except for accidental - no call. If there is even a .5% chance that the play could've been on purpose - the play is no longer accidental and the flagrant 2 is called.