Both the parties have exchanged fires in the past - despite all the communication in place. Both the parties have had losses in those fires too.
Such things happen in times of war, and yes - they are accidents, they are not deliberate actions, and they are not rare either. Remember how Pat Tillman died? That's a famous case - you must know. The NATO troops had great and sophisticated modes of communication between them, yet accident happened. Sinking of Seawise Giant? In fact quite a few times Pakistani troops too have killed their own! And so have others.
AM, I am not giving out judgements here. I am not saying Pakistani troops were harboring terrorists, and I am not even saying the fire from the chopper was to cover the infiltration of terrorists into Pakistani territory (It would be stupid to not just fire, but even kill so many simply to infiltrate the terrorists). But I strongly feel you are judging a bit too quickly, with nothing but your own speculation fueled with your bias in favor of Pakistani troops.
Patriotism, yes I understand it is a very powerful emotional force, but unless you know all the outcome of the investigation reports beforehand, or unless you were there at the post as well as in the chopper at the same time to witness everything that took place, you shouldn't be throwing such accusations with the confidence you show.