Yeah, if the plane was REALLY at 31,000 feet... As far as I know, the best of the MANPAD types have a maximum altitude of around 26,000 ft. We know Hillary and Barry were passing out MANPAD types to terrorists like candy to kids on Halloween..
Did they also pass out some of the larger types that can reach that high?
Or have the Chinese sold them some of their bigger ones (They are selling them to Turkey).
But easiest answer if the plane was beyond MANPAD range is that Ground crew snuck an altimeter or radio controlled suitcase into the baggage compartment.
That is my best current guess.
The article says that a satellite detected the heat signature of the plane exploding, but saw no heat signature indicating a missile.