In the early 1900's his quote was exactly correct.
However,,, as times have moved from the 1900's to present, that is no longer the case. Don't misunderstand, I WISH it was true. But the reality is, you can no longer go to the bank and exchange the "IOU" for the gold it represents.
In the real world, it is now accepted that the paper money is in fact the true money.
You and I will always have to pay back the IOU's where the government does not. They will either print more money or sell bonds to generate money. The issue with the selling of bonds is, when it is time for you to cash in your bond, they will simply sell more bonds to generate the funds needed to cover your bond.
We are now a paper world, that is reality...