Just because he's gay doesn't mean he supports marriage equality. Given Thiel's political views I would guess that he thinks that the government shouldn't care

Just because he's gay doesn't mean he supports marriage equality. Given Thiel's political views I would guess that he thinks that the government shouldn't care about _anyone's_ marriage, gay or straight. So rather than fight for marriage equality for gay couples he'd fight for marriage deregulation for everyone, including straight couples (e.g. no special tax treatment, no special legal protections for spouses).