Well, Francis has certainly done his bit to contribute to the destruction of marriage. And his actions have done everything to encourage the gender stupidity. Inviting transsexuals ("married" to a person of their original biological sex) to the Vatican to "support" them when they complained about their parish priest not "accepting" them (and making their bishop pay their airfare!), giving audiences to "married" homosexuals, not opposing Italy's radical pro-gender confusion laws, installing quickie divorce procedures and forcing the bishops to go adopt them in their dioceses - the lie is endless.
In short, I'm never sure what he means when he says "gender theory" - maybe he means he opposes the traditional natural law understanding of sex and gender.