The result from the Christopher Conselice of the University of Nottingham is based on the number of galaxies that could be visible to us. This is not the same as the number of galaxies that exist "today", since when we look into the deep space, we also look into the past. We can think of a "light cone" that stretches out in space-time. The number of galaxies means the number of galaxies on our light-cone. This makes sense because the value 200 billion, or 2 trillion, is the number of galaxies in the observable universe. (The entire Universe may be infinite)
The conclusion is that in the Early universe, galaxies were smaller, dimmer, and more numerous. Over time these small galaxies have merged to form the large galaxies that we see in our local neighbourhood.
Now it should be noted that this is a model based conclusion. Conselice has looked at the distribution of galaxies at different distances, and hence different times, and used a model of galaxy formation to infer that at great distances (and early times) there are a great many galaxies that can't be seen. These distant, early, small and dim galaxies greatly outnumber those that can be seen. The conclusion is that there are many more galaxies on our light-cone, but most are invisible.
Since these galaxies are small and dim they contain fewer stars. There is no change to the estimated number of stars or to the estimated mass of matter in the universe, only to the distribution of these stars in the early universe.