I'm sure soldiers, ever since there have been soldiers, have hooted adolescently in the throes of combat. What would we expect, that they'd go about their work gravely, constantly reminding themselves of the seriousness - the mortal seriousness - of the things that they do, the weapons that they discharge? That is undoubtedly too much to expect. The stupid talk and yells undoubtedly represent a release from the psychosis inspiring and inspired actions that they are committing.
It is not new, it is not groundbreaking, to think: "They sound like the subset of students that you see hooting and unawarely spewing stuff they heard in a movie somewhere. They always talk like this, yell like this. They likely feel most themselves when they most completely give themselves over to the canned material they have been served, night after night, for their entire lives."
What we hear is not the organic, the militaristically gnomic, the earthy - it is the sitcomedic. MTV trashtalk, some Full Metal Jacketisms (Kubrick would have loved this, at least in a way) thrown in.
And, because you too have seen the same movies, at least a lot of them, you are able to try to reconstruct any possible reason, any scenario at all, in which the cars that speed in, crash, disgorge their occupants, who then are blown away by the Americans. The sniper was in a car? The insurgents, after a lengthy pause, get into their little cars and attempt, as an act of insane bravery perhaps, to speed past the marines' position? Why?
Unlike the talk, no, the actions of the "insurgents" don't fit into any plausible script, especially not the one posted at the end of the video.