Being a "sniper" if I get it right is not a rank. It can be a job description but what was the real job description of the person in a past job is irrelevant for most people in the world. The caption would have been incorrect if the person portrayed actually was a Marine. A sniper would have a different weapon than a "non sniper", perhaps a different uniform, some marks indicating his speciality etc. and the caption would have been wrong. The qualification of "sniper" refers to the former activity of the person. I think the image would have worked, in a sense, much better if the caption had said the person was a former milkman. A former soldier would have a higher inclination to keep a rifle at home than a milkman.

The portrait is - I suppose - somehow necessary in a reportage to make the product more complete. A reportage "tells a story" and has to have a variety of images. Some of them "dramatic" (the action caught in the moment) and some "background filler". In the case of Rochester, abandoned Kodak structures or derelict houses might tell a story about a town in crisis which in turn gives a background information about the rise in criminality. The derelict house or the abandoned warehouse can be anywhere in the world, but constitute a normal "background" image for a reportage.

What surprises me, in general, is why a portrait gets so much attention - I mean before all the fuss.

The "Afghan girl" by Steve McCurry is a portrait in an interior. Isn't that "posed" as well? It's a portrait being part of a reportage.