How on earth did you just randomly find a bison tube (or that is what I'm guessing you found)? I'm impressed.
But to answer your question, it could belong to another site, it could be part of a multi or mystery cache you haven't found yet, it might not be published yet, or it even might be archived. All options- no clue as to what the truth of the matter is.
Actually I was looking for another cache and looking for morel mushrooms at the same time. I just stumbled on to it. It was actually put there in 1971.