People are asking why it would be running a very bright light. Multiple reasons, could have had an emergency for all we know. But most likely, would be to keep its silhouette from being seen from certain aspects from the ground. Bright lights are established practice for concealing classified aircraft, especially on the ground. Doing the same during lower level transits over areas where people could be watching would make sense. Thermal it won't help, but to the eye and low light/nv scopes it would.
Cropped version of the “new” Area 51 test article flying footage.