A. J. Strata has examined the information and asks Exactly What Happened On The Pakistan-Afghan Border? Did We Uncover Taliban Allies Inside The Pakistan Government?
My conclusion is the incident actually exposed a much rumored ISI mole who is working for the Taliban, and seems to point to a situation where the Frontier Corps manning the outposts are manned by Taliban allies who probably provided cover fire for their retreating allies and attracted US fire.
He concludes that
First there was the attack, then the counter-attack, and then the cover fire from the outposts directed at US and coalition forces, making those outposts legitimate targets. And I think when the dust settles it will be discovered ISI sympathizers (like the one who was the source for the AFP story) helped Taliban agents get slots in the Frontier Corps so their comrades could slip across the border and execute raids.
You can see video of the attack here
UPDATE, Friday 14 June
The dark frontier.