This analogy is so wildy off the mark. In fact, an opposite scenario is more apt; a transfer of bitcoins is like handing someone a bag filled with cash, and then announcing it to everyone else in the world so that we can all agree on who has possesion of what. Only now you have a robot or other faceless surrogate perform the transaction for you, and (ideally) nobody knows which surrogates, or addresses, map to which people. The fact that Krugman's analogy botches the primary mechanism that makes crypto-currency work is disappointing.
Edit: wording.