Let's take a cold, hard look at exactly what kinds of things the novel's narrator is describing. There's a woman who keeps her grandson completely imprisoned in her house. There's a man who allows his daughter to be taken away and locked up in a convent for the crime of having a boyfriend. There's a guy who is slaughtered by a bunch of orgy-loving kids he befriends. And there's a whole truckload of incest and pedophilia thrown in for good measure.
To get a sense of the way this narrator works, let just say for a minute that this book was written in, say, the nineteenth century. Supposing half this stuff even made it into print, what would we get in terms of the narrator's involvement? Most likely a huge lecture about how horrible these people are. That's if the author were going for a Dickensian or Eliot-like sort of flair. Or maybe we'd see lots of quips about the downfall of society in general and these characters in particular, and how some of their desires might make us think twice about our own. That would be a lighter, satiric touch, a la Thackeray or Trollope.
What we most certainly wouldn't get in a nineteenth-century novel is a narrator who just sits back, tells what happens, and doesn't seem to have an opinion on the events one way or the other. And that's exactly what we've got here: a lot of beautiful descriptions of who and what, and almost no sense of how or why. Things happen because they do. People act the way they act because they do. The narrator just sits back, records the whole thing, and doesn't ever break that neutral poker face.
This narrator would be considered omniscient from a purely formal point of view. Why? Because he has access to all the characters' thoughts. A completely objective narrator would sound like a police report, with very little ability to describe the characters' personalities or feelings. So even though the narrator strictly avoids taking a hand in the narrative, he does tell us about the inner lives of the people in the story.