Actually, my first project was something called the 8 Hour Baby Blanket, in which you knit with 2 different strands of yarn. So in this pattern, when it said, "join 2nd ball," I thought it meant for you to join another ball and continue with the 2 strands from that point on.
It's just a newbie interpretation. Kind of like new English learners trying to figure out sentences like: "The bandage was wound around the wound" or "They were too close to the door to close it." Only makes sense if you've been at it for awhile. That's why folks like you are so special; you take your time to help new learners like me. Thanks.