I concur with Flying Bull, but I'd like to add that they are discussing in the report if whiteout conditions could be to blame.
It is not quite clear how the fun flight ("everybody on-board was in high spirits") actually ended: "the pullup in front of the ice followed by a push-over and a steep descent that had been terminated - here ended the memory of all eye witnesses" (interesting how the human brain shuts off, or omits the memory after an accident) - probably caught the steep descent, and didn't realize his close proximity to the ground and dug a skid in.
The ride the pilot gave his pax was obviously a little rough though, considering that the mast-moment light came on on the pullup.