Over the Moon
On a practical, real, everyday level: no, there is probably no woman whose period always comes when the moon is full. Unless she is a werewolf perhaps. But on a more spiritual level, there is some kind of a connection between menstrual cycles and the moon. The Greek philosopher Aristotle claimed: “[T]he menses tend to occur naturally during the waning moon […]. For this time of the month is colder and more humid because of the wasting and disappearance of the moon.”
In Ancient Greece, people believed that the mystical link between the moon and the monthly menstrual cycle make a woman on her period especially spiritually and mentally powerful. Poets, philosophers, and scholars have been fascinated by the connection between the menstrual cycle and the moon for ages. If there is such a connection or not, we don’t know for sure. There are different theories on this. But while this guy’s assumption was not strictly true, maybe he just had a poetic and spiritual soul. Nothing wrong with that.