Looks to me like a failure initiated on the aft side of the strut and proceeded forward around the circumference on both sides. The strut would then have bent forward and torn a tab of metal off the top portion of the strut. Friction would then have brought the detached strut aft, still attached by its linkages as the weight transferred to the engine pod. Such an initiation point would likely be caused by some minor prior damage to the strut outer surface.
We'll have to see an up close view of the fracture to know for sure.
If it had been a strut explosion (due to hydraulic fluid combustion) the strut would likely have been 'shivered'.