This is not even the first paper by Dorit Ron and Shamir on Bitcoin; they did an analysis of the transaction graph earlier: http://eprint.iacr.org/2012/584.pdf And that one too was quite poorly done; from the text, it actually seemed like they thought that "the blockchain" is a file stored on blockchain.info. Disappointing from the inventor of Shamir's Secret Sharing and differential cryptanalysis.
People seem to confuse that a lot. It's a badly named service at the best of times. I wonder how many legal requests the site will get from people believing they run Bitcoin.