All sorts of objects have been used as money in the past.  For a long time, (special) sea shells were exchanged as money tokens.   I agree the main requirement is that value is not easily disturbed.

However Dollar does qualify as money still, its just not a very good container since it has become compromised by central government.   The original dollar was based on a silver standard before linking to a more steady gold standard.   It slowly left that idea and the physical part now is only cotton notes which are worth less then the cost of making them.

Dollar is digital as much as Bitcoin is.  The vast majority of monetary exchange is done without any physical token, but the difference to Bitcoin is that value of dollar comes from a central body who can at any time devalue all notes in existence to their own favour.   To compare Ripple and Dollars would be quite close, the value of Ripple relies on the integrity of just one company who can seize value from any holder as they wish though I believe some consensus is required over the network also so perhaps it has some utility over dollar also.