Tethers are essentially IOUs pegged to USD. While the Tether organization may have originally waited for the Tether purchaser to transfer the money into their accounts before issuing the Tether, by 2018 at the latest, this has to have changed when Tether was forced to cease dealing with US citizens. If not from the start, their model of trust must have allowed their large clients (the exchanges, etc.) to hold onto the USD and instead issue "Commerical Paper" to back the Tethers issued.
Tether obviously isn't going to reveal the exact arrangements here, and from the outset, their claims of having bank accounts with billions of dollars was suspect... but this revelation has been nothing new, and if anything, things look positive now. Tether doesn't appear to just be printing Tether with absolutely no backing.
