He definitely could have unwound his positions quietly over time. He'd have moved prices, sure, and his profits would have been less than what was marked to market, but nothing would have crashed. Forced selling from margin calls is what crashes prices.
My impression is it is not at all clear that he could have unwound in a profitable way. If he could have, why did he miss the margin call? He was leveraged to fuck and sunk every little price increase into further leverage.
With the caveat that I am certainly no expert, my understanding is that he blew up when VIAC issued a secondary offering, which flooded the market with new shares at a lower price, triggering a margin call then forced liquidation. So there was an exogenous shock.
Of course, the kind of mindset that would have him take profits is not the kind of mindset that got him to such leveraged paper gains to begin with.
