The #4 answer may be as simple as Ferris having a bunch of options expiring (eg 10 years) so he did a cashless exercise of selling enough to cover the exercise costs of the conversion quantity. However if this is the case we would usually see the correlating acquisition notices as well.
He may also have submitted those sales in an insider sell-plan just to diversify his holdings for wealth management, and is now kicking himself with missing the run-up (exactly why insider sell plans are required in advance).
Or, maybe he is buying a new house and needed the cash. We will likely never know for sure.
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