Any country can print more currency according to Modern Monetary Theory. Also, from Wikipedia:
"The production of Soviet rubles was the responsibility of the Federal State Unitary Enterprise, or Goznak, which was in charge of the printing of and materials production for banknotes and the minting of coins in Moscow and Leningrad. "
If you are trying to draw some sort of conclusion from the idea that the US is an international reserve currency - that has nothing to do with printing money. You can further read the "Economic role" section to understand that the USSR currency was not pegged to PMs or baskets of securities, making it easier to "just print".