Actually, many scholars dispute the claim that Vajrayana appeared in the Buddha’s lifetime. They say that it took form in a number of scriptures that were composed from the 3rd to 12th centuries CE.
Nonetheless, the Vajrayana doctrine of the Three Turnings of the Wheel are a way of explaining that Vajrayana is the final and most complete version of the Buddha Dharma, since it includes Theravada and Mahayana truth, but adds its additional esoteric (mysterious) teachings of the Dharma.