The Taliban cause casualties by indiscriminate fire during attacks
I'll expand on what you mean by "indiscriminate fire". It has cultural significance and interest.
The Taliban are poorly funded (they use the income from the local poppy fields to fund their operations) and are mostly only locally organized. They have limited munitions so you'd think they would use something like the "one enemy one bullet" concept but that isn't true. Often they use the "spray and prey" method.
Us forces first saw this technique used in Northern Afghanistan in the beginning operations. They saw enemy combatants, Taliban, shooting their AK47 on automatic above their heads in a sort of sweeping style. Obviously not a very accurate way of shooting a rifle!
When Taliban prisoners were asked why they shot this way they responded that if they shot accurately to kill a man they would then be forever responsible for that man's sole (a great burden, apparently). So if they used the spray and prey method if they killed someone, it would be only by chance, not intention and the shooter not responsible!
I'm going to guess that this boy's wound came from an AK47!