In mythological stories, details such as this one are never a mere coincidence. Either they foreshadow an event or prepare the mood for such an event. In this story, the fact that the lovers have chosen to meet at the tomb foreshadows their death. Also, it is not just any grave, but the Tomb of Ninus, the well-known and admired founder of Nineveh. It foreshadows the fact that the two tragic lovers will become well-known themselves.