That is misleading. Banks are no longer required to hold a certain fraction of their deposits in their bank account at a Federal Reserve bank--that's the reserve requirement that was reduced to 0%. Keep in mind that only money in the bank account qualifies as reserves that requirement; a literal pile of dollar bills would contribute not one cent.

Instead, banks are required to keep on hand sufficient equity for a percentage of their risk-weighted assets--money that, if the assets go to 0, can be raided to make up the losses. The requirement here starts at I believe 8%, and increases if you're a more important bank.

(If I'm computing it correctly, Tether has disclosed a capital ratio of approximately 0%, FWIW. Were Tether actually held to the same standards as a bank, Tether would be considered dangerously undercapitalized if not outright insolvent.)