in complete disregard of the mandatory requirements for descent.
prospector - it is not quite clear to this dull knife which mandatory requirements you are referring to here, do you have a reference? As Pauline Hanson might say "Please explain".
really believed that they were in VMC conditions
You can have whiteout and be in VMC conditions. VMC is only defined in terms of class of airspace, altitude, visibility and distance from cloud. There is no requirement to have a horizon. The photographic evidence is that they were in VMC conditions. Chippendale said
" Those who have not experienced whiteout are often sceptical about the inability of those who have experienced it, to estimate distance under these conditions and to be aware of terrain changes and the separation of sky and earth."