As per terms of settlement with NYAG, Tether will be disclosing details of their reserves on a regular basis from now on to NYAG, let's see how fake USDT is - NYAG seem satisfied for now that it is backed by full reserves.
Disclaimer: I own zero USDT and an insignificant amount of USDC, being rather skeptical on "stablecoins" in general.
That reserves don't add up to the currency in circulation is somewhat similar to a central bank but the similarities end there and they are basically nothing alike.