An omniscient narrator tells the story of The Boy and The Man in The Road, but we'd be short-changing you if we didn't say more. Sure, it's third person – but it's a third person that likes to shift into the head of one character. Often it sounds like The Man is narrating the novel. Whole paragraphs describe his thoughts, memories, and perceptions. Then it'll pull back, though only briefly. We picked out a passage to illustrate:
He [The Man] woke in the morning and turned over in the blanket and looked down the road through the trees the way they'd come in time to see the marchers four abreast. Dressed in clothing of every description, all wearing red scarves at their necks. Red or orange, as close to red as they could find. He put his hand on the boy's head. Shh, he said. (141.1)
The first sentence describes The Man waking up. But then the narration pretty clearly shifts to what The Man is seeing and thinking. It doesn't read, "The man saw the roadagents dressed in clothing of every description..." but rather, "Dressed in clothing of every description." It's more immediate, and we forget The Man is seeing all this – we simply see it through his eyes.
Third person omniscient narration allows McCarthy a good deal of freedom. He can rove from one character to another, to more objective descriptions of a setting, and to lyric descriptions no one but an author would think or write.