It happens for both the ball and backpieces. If the ball goes in the net with 5 pieces of the board in play you get 5 points, it is just the backboard pieces that goes in the hoops acts like a ball.
A tip is once you know the ball is going in the hoop call another ball (with the right mouse button) immediatley so you can get points faster. Especially on level 2 when there has to be one ball out at any time, you can dictate when the ball comes out at that point. Juggline 2 balls at level 3 is a lot harder but gives you 3 times the points, just try not to drop any balls and have a good backboard and you will get loads of points.
Hope this helps and thanks for helping out it means a lot to me <3