Someone mentioned it but the uncle is telling him the story after Yoke's parents died, so basically telling him and teaching him about death and reincarnation through an old myth makes sense.No pulling out the uncle tells a story that MC suddenly remembers when meeting said death god... First question, why is the Uncle telling MC this story when he's so young? For what purpose? Why will it one day save his life? This wasn't foreshadowed or anything, this is the author pulling all this out of the ass to get an explaination and have it resolved quickly.
If it was really planned we'd have had more foreshadowing to this death god then just "Suprise I'm a deathgod oh now heres a backstory quickly that uncle tells MC about how to trick/placate her out of nowhere".
The idea of our loved ones being reborn and happy after death is quite a comforting thought for a child.