It was shot down, likely from a boat and with a shoulder-fired missile.
It likely wasn't a "shoulder-fired missile" -- for two reasons:
1. The maximum altitude for a shoulder-fired missile is 13,000 ft. TW800 was at 14,500 ft when it began to disintegrate.
2. The explosive charge in a shoulder-fired missile is insufficient to cause the destruction of a plane the size of a Boeing 747.
A boat launch is likely. But it would need to be something a little more substantial -- and more lethal -- than a Stinger.