Alright I thought about it for a bit and here's my opinions from a meta perspective.
At first I was like "really, last second Ghost Rules? That's a lame ending." Then I thought "maybe as the storyteller, he wanted to believe that his parents really did love him but he remembered at the end that he was telling Ghost Stories." But then the foreshadowing in the first letter with DAD KILL MOM contradicts that.
But he's telling these stories out loud. How the hell would he be able to foreshadow that in his telling? Emphasis on certain syllables? What other stories placed more importance on indescribable visuals that could not translate to the spoken word without revealing too much or too little information? As we the audience are the stand in for the beast, what version of the story is the in story beast he is telling it to getting, the audio or visual version? Do these differences propose different interpretations of the story then?