Not Nightowl
... basics of airmanship is situational awareness ... to make an informed decision the PIC needs to have the necessary training ... where does "whiteout" fit ...
Had this PIC been tasked to land that would have been an entirely different matter, the balance of blame might have shifted to AirNZ - "necessary training". But he had received (1) sufficient training for overflight and (2) explicit instructions about descent below MSA, which he disobeyed without sufficient knowledge, cause or care.
Had the AINS not been reprogrammed he might have got away with it. That wouldn't have made him right, it would have made him lucky.