No you don't. That's not how wars work. Secondly, you can't fire on someone from 2.5km away. Do you know what the range of even the most powerful guns are?When you are facing gunfire ,directed at you, you do no stop to think if that is friend or foe. Your reflex is shoot back and if not able to match the firepower call for re-inforcements.
They are not contradictory if in case the Pakistani soldiers were giving covering fire for the running Afghan Taliban who were pursued by the Afghan/NATO troops. That would satisfy both 'accounts' of hot pursuit and self-defence.
Ofcourse you have to accept this is one possible scenario.Infact it can be the most plausible scenario.
I'll show you the obvious contradiction in the accounts: the reason why helicopters were called. One account says that the helicopters were called in because Afghan troops were being fired upon. The other says the helicopters were involved in the operation from the go.