Very sorry to hear that, the-grt-waldo. It's hard to believe anyone would be so nasty as to filch the cache of a long-distance hiker. But if it had been an animal, chances are they would not have dragged it more than a few feet out of its hiding place before busting it open and helping themselves. This sounds like it was taken clean away.
Maybe the person involved thought they were 'protecting the wilderness' by removing it, as if it were nothing but abandoned trash. Except that spot is not within the wilderness boundary, and anyone with sense could tell it had not been opened, yet, by the person who placed it.
The only other possibility I can imagine is a combination, where an animal ripped it open and a person cleaned it up later. Seems far-fetched, but not impossible.