The article is not clear about the details. As far as I know options have a fixed expiration date. Shares don't. It's not clear when the options he exchanged for shares were supposed to expire and which was the market price at that moment.
The marginal utility to someone at his age between 2 billion and 10 billion is functionally identical.
I'd contend his switch was very logical and turned out great for him.
I also threw out 10 billion, and so did you. With the magical hindsight-looking-glass any of us could invest in the right stocks 10 years ago and make a killing today. Big deal.