This is non-news. The sale was "part of a previously established trading plan" -- VCs set these up all the time to slowly sell off shares in a way that's not disruptive to companies. If you owned 10% of a company and sold all that stock in one swoop, you would crater the stock price and piss off employees. Thiel had already sold over a $1B worth of shares by 2016 and FB stock is up 60%+ this year.