Effective ice protection is quite recent. Before that all leaders were effectively soloing--roped or not. (This was also true of rock, just a little earlier in time.)
A friend told me (in ~1980) of climbing Pinnacle Gully around 1970? and the only trust-worthy protection was rock pitons. (He knew exactly where the placements were...)
Also good ropes only became available after WW II.
Unroped soloing is unroped soloing, rock or ice. In either case all it takes is a falling rock or chunk of ice, a break-away hold, a stumble, a momentary loss of concentration, or a single bad move to cause a long and possibly fatal fall.
Note that the report does not say whether:
* the avalanche was natural and swept the climber away
* the climber triggered the avalanche and fell with it
* the falling climber triggered the avalanche.
The avalanche advisory was moderate (natural avalanches are unlikely and human triggered avalanches are possible), but Odell and Central (which are adjacent on both sides) were listed as being at the high end of moderate due to wind loading.
Doug