>Can someone please explain to me how a “libertarian” like Peter Thiel could start and run one of the most anti libertarian companies? What are his beliefs, exactly?

None. He is a slimy character with no principles or morals besides his own selfish drive. He wants to make money, period. Other considerations don't factor into it. Make no mistake, he (and people like him, the capitalist sociopaths that hold power in our society) would kill your entire family for a handful of pennies if they would get away with it.

If there were any justice in the world these kinds of people would be shunned and censored by society. Yet it's precisely the opposite. These are the behaviours which are encouraged and rewarded.