There was a large explosion, about 2 perhaps 3 seconds prior to impact as seen in the video.
Isn't it quite possible that if a portion (or all) of a wing failed at that point due to aerodynamic forces, that the rapid release of fuel in the slipstream would create a fireball which could be perceived as an explosion? Much like the fireball which erupted at the breakup of the Space Shuttle Challenger was caused by the failure of the main tank. In that case, It appeared to be an explosion, but in true defined terms, it was not.