https://www.hollywoodreporter.com/news/peter-thiel-facebook-...
Notice that at the time the article was written he had sold about 37 million shares and had only 5.6 million left. The prices he got were absolute peanuts compared to the current price -- he sold 17 mln shares for $38, and another 20 million for about $20. The current price is $180.
I am not writing this to criticize Peter Thiel, obviously the stock market is very difficult to predict. And, unfortunately, I did not buy FB at $20, so I cannot say I had a better mastery of the market than him. The point I want to make is that is downright silly to make any conclusions about FBs valuation based on this sale.