It boils down to this: You take a bowling ball, and put it 1 meter stick away from you at zero velocity compared to you. Assume that at this distance, no forces

It boils down to this: You take a bowling ball, and put it 1 meter stick away from you at zero velocity compared to you. Assume that at this distance, no forces are exchanged between you and the ball. You wait a billion billion gazillion years, take your meter stick again and measure the distance between you and the ball, and notice it is now 2 meters away. It is the distance between you and the ball that has grown. Note that the ball has not grown twice its size. The sizes of atoms and molecules have not changed (as they have mechanisms to keep them exactly the size they are, despite space growing). It is only when there are no mechanisms or forces to keep distances between objects fixed, they seem to drift apart very slowly. The question the article addresses, is whether that growth is accelerating or not.