MG42s or MG3s were not supplied in large numbers to the Muj. Those people keep every gun they get their hands on. We would have seen them in the civil war and the current war that started in 2001 if they had them.
Iran and Pakistan have borders with Afghanistan, the terrain is the same in those places. The people look and dress the same. OBL was a Saudi and he looked like one of them. So, you really can’t tell what country it is by the terrain or where the people are from by the way they are dressed.
If the film clip was taken in Afghanistan in the 80’s, the MG was probably taken there by one of the many foreign fighters, the “Afghan Arabs” who went to Afghanistan to wage jihad against the Soviets.