MANPADs and Stingers can't reach that altitude of 33K FROM THE GROUND.
From an ultralight or mounted on a Piper Cub? Maybe.
Also, some of the data indicates it was still climbing to it's cruise altitude, not yet at 33,000 ft.
I wouldn't totally rule out a MANPAD just yet.
The altitude graph of the plane crashing showed that the "ground" was at 10,000 feet. The crash site has been described as a "mountainous area".