That's a reasonable assumption. But if they were taking fire from an apartmetn or house, they have every damn right to not only shoot first and ask later, but to level the damn house. The incident in Pakistan was a prime example. Yes, we killed "civilians" when we bombed out an Al Quaeda meeting. Too bad. Don't associate with terrorists if you want to stay alive.
These are US Marines, and I will afford them every benefit of the doubt until they are convicted. Hopefully, that will not happen.
I don't think we will ever get the real truth on this story now. too many political agendas and egos to be fed surrounding it, too many people who need/desire the worst possible accounts of this story to be true, to allow an accurate account to be obtained.