The size of the trade, the change in implied vol, and it being late in the week, all would have involved a supervising officer of MS to sign off on the position NOT being closed, versus the amount of cash actually placed in the account before the trades took place. MS is assuming the risk for that magnitude of trade. Cash account or not. It would not matter, size does. Someone at MS should've wanted extra "good faith" cash to mitigate the risk.
UNLESS, the bona fides of the account owner's ability to raise Institutional levels of cash ($20 Million, at least, usually in TBills, or 10% down), on demand, was already known to MS. That's what an officer could sign off on, before leaving on Friday night, for the weekend.