They are saying it got to 30-35 thousand feet, then came down and tried an emergency landing where they came apart. I don’t think ISIS has weapons that go that high. Could very well be a maintenance issue. Either that or a bomb or sabotage.
Airframe failure is not unknown, but there certainly are SAMs in the area that ISIS could have that reach several times the 35K altitude.
The whole middle east is awash with weapons, small and large. If it can be carried on and fired from a truck, it can be in the Sinai. S75s and S125s litter those countries, including Libya and Egypt.
Or, as has happened with Airbuses before, the damn tail came off.