Understanding CN0326 Layout

Hi,

I have been studying the layout of the CN0326 reference design, and I wanted to clarify the ground layout 

Top layer DGND pour 

Bottom layer DGND pour 

So I have uploaded two screenshots  the first screenshot is of Top layer DGND pour in which I have used highlight too in the OrCAD PCB designer and I have circled the text which says that highlighted net area belongs to DGND and I have also circled the layer  under the visibility tab on the left side and I have done similar thing for the second screenshot which of bottom layer.

My question is why was DGND was poured on top as well as the bottom layer of the PCB and traces were passed throguh the DGND layer on both top and bottom layer, whereas to just pouring only the bottom layer with DGND and connecting the top layer componets and traces to DCND with vias. I also observed similar techquie executed for the isloated part of the PCB in which AGND was poured on top as well as bottom layer and then traces were connected through the pour. 

I would like to understand the reason why do we do that and what are the consequences of not following the practice if that is what the designer has done, please correct me if I had got anything wrong with my understanding.

Thank you.