Not an accident. An accident is when some idiot leans against the control panel, hits the red button unintentionally and goes "Oops! I shouldna done that."They can't see the plane. It was 35,000 ft in the air. Radar picked up a plane and they prob assumed it was a Ukraine transport.
My guess is that it was an accident as no one has any incentive to shoot a foreign civilian plane.
This was a deliberate act. Some idiot shot down the aircraft he was aiming at, he just didn't know what he was aiming at (that's the idiot part).