So who are the strangers in your dream? Are they just people you've seen in your daily life? Your subconscious mind remembers them and uses their image as need be. Then I could possible be a stranger in someone else's dream.
What if the subconscious minds could interact with each other and that makes the extras? I've personally had dreams that I've felt out of place and distant merely looking in on someone else's dream.
The extras in the background always seem foggy and the faces are usually hard to make out. Sometimes they even seem to be motionless. Time seems to not exist. Almost ghost-like. What if that is it? Ghosts? It's said that spirits are usually not seen by the conscious mind but maybe the subconscious remembers them. It would explain the disarray of the strangers. And how distant they seem, even if you have some interaction with them.
Maybe a dream is like a movie for ghosts and other subconscious minds to watch. They're just spectators poking around in your mind. Just strangers.