I think at this moment in time, we just don't have enough information to form any sort of reasoned conclusion.
ISIS claiming responsibility by itself isn't enough to convince me, since they and their irk claim responsibly every single time an American or coalition aircraft goes down, and most of those times, it was latter discovered that those claims were bogus.
There are simply far too many possibilities.
If the plane suffered catastrophic mechanical failure and entered into an unrecoverable dive/stall, the G forces involved could have snapped the plane in mid air.
A bomb could have went off and caused the plane to break up before the pilots knew a bomb had gone off, in that instance, they would have just been going off of what their instruments told them, which could have resulted in the report of mechanical/technical issue instead of bomb blast.
A missile with proximity fuse could have peppered the underside of the plane with shrapnel. The pilots would have only felt the impacts and rocking, and with fault indicators lighting up, again, they could again have reported only mechanical/technical issues, and gone down before they knew what really happened.
The fact that a large part of the plane appears to have gone up in flames before or after crashing would undoubtedly complicate the process involved in determining exactly happened.
And those are just a few off the top of my head.
The best thing to do is wait for solid facts and not jump to conclusions.