Gross simplification having read the report this morning.
The final cracking was probably caused by the manoeuvring to land on the mountain side. However the crack would have been propagating for some time, at least since the last visual inspection. The MRG SC is an un-lifed component so wasn't captured in the recovery programme when it was realised that MoD's interpretation of the aircraft limits was wildly different from Bell's* and a recovery plan had been initiated to get everything back to a safe condition (this was in ~2009).
So definitely some element of luck in that the manoeuvring to land caused the final over stress, but the crack would have been growing for some time.
*Bell basically said 'Aerobatic manoeuvres prohibited' which MoD turned into a 90 degree pitch and bank limit. Bell later revised the Flight Manual to read something like 45 deg of bank and +30 -15 pitch, which resulted in MoD having a bit of a panic attack.