Why isn't this film categorized as fantasy? a spooky bedtime story to scare kids into sleep?
To categorize a film as a mystery/thriller you have to have elements based on real life. Schizophrenia is one thing but seeing dead people and predicting who died in an accident isn't a real thing.
To draw a parallel, let's take the Edgar Wright latest film last night in Soho. The protagonist wannabe fashion designer is seeing visions of London in the 60s. Hence, the horror categorization of the film.
The Sixth Sense doesn't have much horror to it save the dead people that appear before the child prodigy, that's why I thought fantasy would be a more fitting genre.