You're uh... aware that the photographer didn't sneak into their room without them knowing, right?
Being back to back in physical contact, even while also engaging in some other activity, is not necessarily (or, IME, even most likely) ignoring each other.
I actually think it's very much part of the message of the particular image it concerns (at least, it's part of what I take from it because of how it resonates with my personal experience), to wit, the whole collection speaks to the pervasiveness of the smartphone in modern society, and the image in question speaks specifically into it's insertion into moments of casual intimacy.