After the dragons were almost wiped out by humans, the dragons went berserk and ate a lot of humans for vengeance.
It was probably where the stories of dragons eating humans originated. Those who witnessed it probably wrote about it or told the following generation and it was passed on due to how terrifying it was.
However, Ferdinand explained that the primordial dragons and those who had lived long enough no longer even required food.
They could simply gather the mana in the surroundings once in a while if they needed to and that could serve as their sustenance.
They have long stopped feeling thirst and hunger.
Ferdinand only ever felt hunger and thirst again when he gained a new body as a human.
It was rather a pain for him to have to eat several times a day, but he found it fun too since he desired food again after not caring for so long.
It was no wonder that after living for so long, they no longer found any reason to live.
They learned everything they wanted.