When you're Thiel, having the money liquid is more valuable than waiting. One way to look at is that he could have 5x'd the money had he not touched it. But I'd bet whatever he did with the money since the 2012 IPO (starting companies, investing in companies, etc) had a much better return than 5x.
The extreme of this would be the Silicon Valley right and its full and explicit embrace of feudalism and monarchy.
... and no, I'm not criticizing Thiel. The vicarious sycophancy of the HN community is a lot weirder and at times more troubling than the behavior of the actual SV rich.
The top post in this chain says that he sold 17 mln shares for $38 and another 20 million for about $20. The stock is currently trading at $180/share. If he had held on to those shares they would have been worth $6.66B today. According to Forbes his total current net worth is $2.6B.
I certainly won't criticize someone for making a diversification play after having already made such a huge gain (his initial investment was $500k) but in retrospect it very much looks like a mistake.
Judging decisions based on future knowledge is utterly worthless. "In retrospect, picking the losing lottery numbers was a mistake. In retrospect, picking the winning lottery numbers was brilliant."
It was only a mistake if it was a wrong choice given the information knowable at the time.