I agree that it is a last-ditch effort by Celsius. The terms of the loan they had with Tether very clearly spelled out when a margin call is triggered. If Tether did not follow the 10-hour notice bit not sure of as most loan agreements do have a 'final notice of intent' for triggering a margin call but most of the time it is at least 24hours before forced liquidation of assets happens.
As for the amount Celsius is suing for - not gonna happen. IF a judge even allows the lawsuit to proceed standard rule of law is for fiat value at the time an event occurred.