Speculation
If the tail horizontal stabilisers had deflected fully upwards instead of down, the nose of the aircraft would have dropped and with the engines set to climb power, the aircraft could enter a mach stall.
Aerodynamic forces once the aircraft broke the sound barrier could be sufficient to tear the aircraft apart, or at least separate the tail section. The sonic boom would sound like a bomb explosion. At lower altitude the remaining fuselage and engines enter a flat spin, causing the engines to tear from the wings and leaking fuel to ignite.
The FBW protection systems would normally operate to prevent a pilot performing such a manouver, but not necessarily if there was a sudden failure in the tail horizontal stabilisers.
Of course the stabiliser might have flipped down first and then fully upward, which would generate the same general effect.