Truth - supernatural isn't automatically horror. Though, ahhg, I was so upset to find horror has been taken out of the book store - there is no horror section. And at the last conference I went to, when they broke into genre, horror simply wasn't an option. Paranormal romance and thriller both were, fantasy and sci-fi, but not horror.
If you read it, you'll see why King had to go back to the character. He tells a story about how he'd be calculating how old Danny would be - he'd just be driving down the road, and he'd wonder, how old would he be? What would he be up to? He isn't a fan of sequels, he says, and doesn't feel the need to revisit other things. Just this one.