Oil rigs producing as much light a large city does not seem unlikely at all to me. The Prudhoe Bay oil field in the north of Alaska has always stood out in its disproportionate brightness and size in any night-view of the earth I've seen (and light pollution is the least of our worries when it comes to this place's environmental impact).

That being said, oil fields being overly visible might be a symptom that they used data based on satellites capturing slightly lower frequencies (near infrared) rather than precisely representing visible light. I know I've seen night maps of the earth that turned out to be based on near-IR imagery.