shit this might be true
He might be the reincarnation of the Sungyeon from the Joseon era, Current Sungyeon's grandpa. I bet he didn't get his happy ending here?
So he's his own grandpa?
The Joseon dynasty Sungyeon's soul was reborn to his grandpa which is why he seems to get memories that aren't his own. There was a previous chapter in the manhwa where current Sungyeon's mom says that he looked exactly like his grandfather and they were all surprised of it. Maybe the soul of the Joseon Dynasty Sungyeon transcended countless times because he was bound to Hosik's soul with that red cloth they attached to that wooden doll.
Could be just a theory though.
Is he Sungyeons grandpa? Or Not?
Because they said the Sungyeon looks exactly like his grandpa.