The assets in question were evidently given to Tether as collateral.
Defunct cryptocurrency exchange Celsius has filed a lawsuit against Tether alleging misappropriation of assets and seeking approximately $3.5 billion in BTC returns, damages, and legal fees.
Up front: Tether reports that Celsius, in its lawsuit, seeks the return of approximately $2.4 billion worth of BTC. However, publicly available court documents show that Celsius has asked the court for relief in the amount of 57,428.64 BTC or its current market dollar equivalent, plus damages and legal fees.
The lawsuit alleges that, during Celsius’ bankruptcy proceedings, Tether loaned it a specific amount of USDT (the company’s stablecoin, a cryptocurrency backed by the US dollar). In return for this loan, Celsius sent Tether 39,542.42 BTC in collateral.