example - Swiss National Bank issues EURO-bonds or PBOC/HKMA issues USD-bonds or EUR-bonds - it is DENOMINATION UNIT which investors count.

maybe looking from another angle PAXOS issues PAXG TETHER issues XAU both hodl underlying asset - very clear in case 2nd country issues BOND in denominated in another country currency do the need hodl asset in that currency or just credibility to settle in that currency ? that's puzzle

so this is what it means seems like "CREDIBILITY of ISSUER" is main thing - even if NOT HOLD asset directly in USD but can settle in USD at redemption/rollover convert non-USD assets like gold or CNY or EURO bonds. for example.