This is probable, but without further evidence the cause could still be terrorism or a defect. The only thing that is looking unlikely is pilot error.
I don't think so. There was some triggering event. Overheating, crushing of glass, arc or short circuit, battery runaway, explosion, smoke etc. It was after midnight, nobody was fresh. Remember AF477 - nobody told "stall", all three were fully confused. They surely knew what the stall is, but in that moment they couldn't see it, they didn't believe computer warnings. In our case the crew might be confused and did some wrong actions too. I hope that they didn't, but experience teaches us that we all do mistakes. We must wait for a more data.
Are there airline crashes at sea where there were no large human remains?
I can remember KE007, MA240