The story behind this video is that a guy was walking to the grocery store and heard a dude singing and playing guitar.  The guy then starts to record the musician because he thinks he's pretty good, then another man stops by and joins in.  After a couple of minutes a third fellow jumps into the mix as well.  What happens next is an awesome random jam session in front of the grocery store.  According to the video description these guys don't know each other and this was a random occurrence.  This could easily be staged, but I would rather believe that this was truly an impromptu jam session.