ANZ's only crime was not doing a proper due diligence, and should be reamed for that.
It wasn't so much that, as Cushing and Brierly having a cunning plan that if they bought Ansett (which Singapore Airlines were looking at) then Singapore Airlines would buy Brierly's chunk of Air NZ to get Ansett.
Unfortunately they proved to only be the smartest guys in the room - and their cunning plan failed and we all know the rest.