I don't argue that it doesn't happen, but "if it quacks like a duck"?

Intent is usually a huge factor in determining the seriousness of a crime. If someone shoots and kills someone who is attempting to murder them, that's ok. If, while attempting to shoot and kill that person, they kill an innocent bystander, that's not OK and usually punishable (manslaughter).

Am I right to infer that your argument is that those two situations are morally identical?

To the village that lost 50 people to the omnipresent invaders, it may just be morally identical. "Oh, hey, we thought you were terrorists - our bad" probably won't cut it as 'understandable', given that 40 of the victims were women and children, which aren't generally part of the insurgent personnel in Afghanistan. Keep in mind that this wasn't a wayward bomb - the innocent bystander in your story - but a target hit three times across several minutes.