Let's say you pull into a boondocking area about the size four city blocks, and there's already someone camped there. Someone you don't know. (Me.) The proper thing to do is find a spot for yourself that grants the first camper reasonable privacy. A hundred yards or so away.
What you don't do is pull up just on the other side of a tree, like this guy in the black pickup did. It's sort of like sitting right next to a stranger on an empty bus. Intrusive. Kind of creepy.