That is not true. They were asking for payment from him all through 2019 and 2020. The problem was they were set to go to trial, and there was no way they were going to do all that trial prep for no money. Plus the relationship was damaged by his continual stringing them along.
Who is holding USDT? Likely traders who went onto Bitfinex (Tether's sister company) and sold their BTC there for what they thought was a good price. BTC, in this scenario, is a bridge to USD, because it can be moved to an OTC desk or a banked exchange and sold for cash.
If Tether were in fact receiving real USD to support the billions in USDT it keeps issuing, then why hasn't it handed over financial docs to NYAG, which is investigating it for fraud? Why has it not had a third-party audit? Why does it keep printing USDT in larger and larger numbers (a sign that the real $$ may be disappearing from the system)? Why don't we see a similar growth in other regulated stablecoins?