ISIS/Sinai State did not say that they had 'shot the plane down' they said they had 'downed the plane'- leaving room for interpretation......
This French article in the Huffington Post has a whole host of 'experts' stacking up arguments for the bomb theory...
Crash en Egypte: un scénario semblable à l'attentat de Lockerbie en 1988 est évoqué par plusieurs experts