As Jack says, it's the "theist version" of compatibilist free will, but you can replace "God" with "the universe" and the point goes through, Aquinas uses God because he's trying to build up a coherent metaphysics. And quite successfully! He gave the "right answer" to the "free will problem" off-the-cuff as if it was no big deal. This raises my confidence that Aquinas is also insightful when he discusses things I don't yet understand, like faith.