Yeah it’s called unreliable narrator is stories like these. I quite enjoy them.
The MC (Huimin) themselves didn't know or understand what's really going on. Since the story progress in his POV, readers will be also confused as he was.
MC is a transmigrator while ML is a regressor, Silence is their original world but MC died and reincarnated in the world where he lived a normal life with ML and he lost his true memories of silence, so basically the entire plot is MC recalling his past life experiences but knowing season 1 author's note, they DID say the plot won't entirely follow the novel so ig they went with the identity disorder route(?)
Judging by how nonchalant Huimin after ML confess everything, I guess he isn't really the same personality as original Huimin. Original Huimin is a normal type that broken by cruelty. Huimin here has a stress free personality. So it can be said different personality.
So he actually has that disorder but didn't know he actually had it? I'm confused.