Elon Musk has definitely seen the potentials bitcoin has after making his analysis, thus calling cryptocurrency brilliant but predicting the end of paper money is something I don't think will occur. Paper money will not end but will co-exist with cryptocurrency. Well I maybe wrong but that's my opinion.
In the short term, but i think he was meaning in the long term. It won't be overnight, people will slowly use less and less cash, and then the switch to crypto is easier.