Unless my math is off, or I'm misreading the article... that's about 1% of his total shareholding he's sold. How is this a scramble to offload shares? It seems more like a pretty minor (and sensible) liquidity transaction.
Unfortunately, "Dustin Moskovitz executes a pretty minor (and sensible) liquidity transaction" doesn't inspire people to click the link and view their ads...
Quite. If one has all (or most) of their personal wealth tied up in one venture, it's only prudent to release a proportion. Of course, where he stops selling will be the interesting part...