Esquire: Snipers in Iraq

Esquire has a fine story about American snipers in Iraq. I know next to nothing about the particulars of the story, but something bothered me:

Hensley said, "If he pokes his head up again, I'm going to take him out." He did not have a high-powered sniper's rifle. He had the basic rifle of the American infantry, the M4. It is basically a .22. The guy across the river was anywhere from three hundred to four hundred meters away. It is not the kind of shot typically made with an M4.

Again, I don't know much about the particulars, but I do know that 5.56 mm is pretty damned different than a .22, as clearly illustrated in the picture above. I also know that shooting a man at three hundred meters or four hundred meters isn't all that hard to do with rifle, even an M4. Hell, I must have killed dozens of prairie dogs at nearly that distance with my civilian M4 and prairie dogs are a hell of a lot smaller than a man. The point is, this is a small detail easy to verify and understand, if the author is wrong on this little detail how are we supposed to believe the rest of the story?