My opinion is that the Blackhawk pilots were either confused or disoriented. That happens at night when spatial awareness is very low if you're not used to it. When I flew in the Marines as a CH-53E crew chief, we always flew "dark" (no outside lighting) when we were flying on NVGs. Once we were transitioning back to base over residential areas and in the proximity of John Wayne airport in Orange County, we turned all of our anti-collision lights on like what you would normally do for any GA or commercial aircraft.
I do not know if they were on NVGs during the flight, but if the lights were off, I have to assume they were.