It would interesting to know just which auto-pilot was installed in that aircraft. I few Lear 24s (oval cabin windows) back in the mid 70s that had the Lear auto-pilot installed, which at that time was the only auto-pilot that was available for the Lear 24, not sure about the 25 series.
I don't believe the old analog Lear autopilot was ever able to receive RVSM certification so the aircraft would presumably have an updated avionics package, including a new autopilot, to legally fly above FL 290 in the U.S. or Mexico.
Of course, in light what has been revealed here so far about Mexican bizjet operations, maybe the RVSM certification for this aircraft was 'undocumented'.