The only option that the author doesn't explore, is the possibility that the WSJ author may be correct in saying that the more robust Android ecosystem is gobbling up market share.
Or even more blandly: Apple overshot estimates for the holidays and has stock on hand they have to sell. There doesn't need to be any "falling off a cliff" or "gobbling up" to explain this. Orders in the just-in-time manufacturing world have always been volatile. That they haven't for Apple is simply because of Apple's extremely rapid growth. Extremely rapid growth isn't sustainable long term. And they're finally leveling off.