What gets me is that the note appears to be heavily circulated, and I suppose that it could have just been from someone found and kept in their wallet for a long, long time too. Even so, I think that it is highly suspect that the note should be in such condition with the obvious errors.
My thought is that it was a curiosity someone obtained somehow and kept it in their wallet. The creases/folds are sharp and it appears that they are not doubled or tripled too much from others missing the mark when they would quickly fold them. A quick look at a five and ten in my wallet show that they have broad folds/creases and that there are crooked ones and off center ones, etc. For a note to be circulated and be in that condition I would think there would be more of that. The wrinkles in the rest of it are common to some papers I have kept in my wallet for a bit too long. The dirty aspect of it, well, maybe the owner was just a dirty little fellow.
So that’s my guess – but Sherlock Holmes I’m not!