It's hard to imagine any material or geometric reason why a turbine disc failure should necessarily involve separation into 3 neat 120° segments. This one certainly didn't:
There may be some confusion with the fact that safety analyses, for certification purposes, around the consequences of an Uncontained Engine Rotor Failure (UERF) are predicated on assessment of the trajectory of a single one-third disc fragment plus (depending on the regulator) a single intermediate fragment and other small fragments.