So, to me it looks like they have just been somewhere together - maybe an outing or an adventure where they didn't have phone access. Their bags and backpacks suggest some shared activity. So I'm guessing they spent the day together chatting and socializing, and now they're checking their phones. That's my take :)!
I don't know if you know the painting " the boyhood of Raleigh" if not google it and open it on the screen with your shot. This is the 21st century version of Millais's picture..
A sure sign of the times! Groups of people using their phones and not communicating with each other! The advantage to a street photographer you can point your camera in their faces and they still don't see you!
