That is correct, all night flights in Mexico are to be conducted as IFR, and the captain had a "VFR only" restriction on his license.
There is a vast number of November registered planes operating in Mexico in similar conditions, a couple of weeks ago the crew of an N-registered Hawker jet owned by a mexican charter company had a ramp check done by an inspector in Houston and they found they were operating under a Part 91 certificate but renting out their planes to the public, copilot had no type rating, only FAA private pilot licenses, and so on...
Another accident that comes to mind is the Lear 45 XC-VMC crash in Mexico City on which Secretary of the Interior Juan Camilo Mourino lost his life, both pilots had a faux type rating on their licenses...