I think the bottom line is that right and wrong are secondary to defensive and careful behavior.
Both skiers might have some fault, but the accident could (possibly) have been avoided by more careful skiing by either of the parties involved.
When I'm driving I don't change lanes without making sure some moron isn't flying up to pass me on my right. No reason I shouldn't ski with the same care.
Like the old saying goes (originally about fights in relationships) "Would you rather be right, or happy?" (or in this case ... or uninjured?")