If you look at the lower, it appears that it's engraved with something resembling the "MK 18 MOD [0/1] // CRANE, IN" markings on the magwell so that would align with it being a Navy rifle and not a Marine rifle.
Funny enough, I thought the same thing about the VCOG. I'd only seen them on IARs and not anywhere else in the Navy so I was a big perplexed how that piece of kit found it's way to a DDG's arms room.
And that last part, agreed. If it comes down to the CO picking up a rifle then things have gone very, very sideways. And the engineers on the civi side say the same thing about PAO/Sales & Marketing types.