If I remember correctly “The Mist” also ends by pretending it was a “historical document”. That’s the similarity I was referring to. In my opinion it’s a bit silly. Are we really to believe someone had time to write entire book while running for their lives? With dialogs and detailed description of all events? It’s also totally unnecessary. You can have an open ending without pretending it’s a historic document. It’s also crazy old. Don Quijote does he same thing, pretending it’s actually a real story being translated from old, Arabic sources. It doesn’t mean the books are bad. It just a trope ending.