[mrandish]

Yep, either the military or a defense-type contractor taking their new toy out for a spin. There could be a lot of reasons they didn't privately fess up afterward (at least that we know of):

* The flight was an "ad hoc training exercise" that wandered a bit too far (ie not specifically approved by higher authority).

* It was a capabilities test to see how well it could do stealthy observing of energy infrastructure in a civilian controlled airspace. While the US doesn't need to spy on its own infrastructure, it's convenient to trial run locally before deploying the capability over Crimea or Venezuela.

* It was a penetration test to measure response to a potential terrorism scenario. If they had warned the airport or police in advance, it wouldn't be an instructive test.