Carver's narration in "Neighbors" is objective narration that is sometimes referred to as "Fly on the wall." Today, we might think of it as similar to a security camera on the wall. The idea is that only what is seen and heard is revealed to the reader. No comment or interpretation is used by the narrator, and no character thoughts are revealed, either.
"Neighbors" is a story about voyeurism. The husband and wife become fascinated and obsessed with the lives of their neighbors. So much so that merely being in their apartment creates erotic feelings or, at least, since we do not have access to their thoughts, creates erotic behavior on the part of the husband, and possibly on the part of the wife--she is the one who reveals the pictures.
It's important to notice that the husband and wife behave normally before we see them behind closed doors with no one, except the reader of course, watching. They are just a normal couple like every other couple.
"Neighbors" by Raymond Carver is usually classified as minimalist and absurd. It is minimalist because there are no explanations—nothing but the simplest language and minimal descriptions of what is happening. It may also be considered absurdist because, even though the actions are connected to the lives of the Millers, they go beyond normality. In real life, most people in the house of a neighbor would find it natural to look about, take a book off a shelf, and look at wall hangings. But could anyone regard the Miller’s examination and use of the Stones’s apartment as normal?