In the Flash/Arrow crossover Legends of Today/Legends of Yesterday, we're introduced to Vandal Savage, Hawkman (Khufu), and Hawkgirl (Shayera). The three of them are bound in a repeating cycle where the Hawks reincarnate, and Savage hunts them down and kills them. At one point, we see the origin of this cycle, back in ancient Egypt.
My question is related to what we see there. In their death, Shayera prays to Horus for help. Meanwhile meteors are raining down upon them. Then the Hawks die, and Savage becomes immortal. What exactly caused the reincarnation and immortality cycle? Did Horus answer Shayera's prayer? Did the meteors somehow cause the Hawks' reincarnation? Did Shayera/Khufu/Savage cast a magic spell?
What caused the Hawkman/Hawkgirl reincarnation, and Vandal Savage immortality?