Good theory for the cockpit personnel problem.
If that's the cse, though, why then turn off the cellphone repeaters and ground phone comms? Possible answer - to buy time, and prevent from being shot down by the Mirages?
Problem with that - time is only important if you're aiming for a target, like a city. And why wouldn't you, if you're a Muslim terrorist? But apparently the goal was just a long, slow descent into the mountains. Doesn't sound like a terrorist target.
You can still cause terror by slamming 150 people into a mountain.
Which would do more damage to the European economy: a random terrorist incident, or giving the impression that Airbus planes will fall out of the sky for no discernible reason?
As far as not announcing a terror attack: perhaps they want to intimidate European leadership, without generating a public clamor to move against Islamists?