You overcomplicate things. There is plenty of liquidity to sell 120k eth; the opportunity cost of doing this is near $300 million
By casting a spell, today they also have 93 000 extra ETH. They are saving some of their potions for later time to cast wider spells.
Jump has stated they now still have 93 000ETH since they wish it it is so.
It might well be that they can eat a $320M loss on the regular, but if so, this situation isn't any kind of indicator of it.