You clearly don't understand libertarians. You think that because his daughter decided to be a boy that he would turn into a flaming leftist? I don't know Penn Jillette, I have never met him but I have seen him in enough interviews to know what kind of a person he is. I also understand libertarians.
I am not a libertarian but I am probably the closest thing to a libertarian. I am a Constitutionalist. Where I differ from libertarians is I don't believe in legalizing narcotics and prostitution.
Libertarians believe in freedom. If his daughter has gender dysphoria then he is more than willing to oblige her because she is free to choose what ever kind of life she wants.
Leftists on the other hand want to force people to do what they want them to do. They hate individual freedom. That is why if anyone disagrees with their dogma in the slightest they are called racists, sexists, homophobic or whatever the insult-du-jour they come up with.