Hmm, he was working with a flat plane instead of a 3 dimensional shape to start with. I wouldn't recommend that
To each his own, I suppose.
Anyway, all he did was select all of the faces from the plane once he finished tracing his reference image, and then he extruded the faces from that to give it depth. Go into
edit mode, and make sure you are in
face select mode. Then press
A until the entire mesh is selected. Now press either
1, 3, or 7 on the number keys so you're looking at the mesh from the top view. Press
E, and then select
extrude region. Now grab the extruded faces (G), and press either X, Y, or Z on the keyboard to pull them out parallel to the grid. Should work
Kravenwolf