no no, he just right click mouse button select faces then go into front view and all u do is just select all the faces on one side of your dog and delete them.
in front view this is easy as u just u the sect rectangle box all the way to the middle. later on he will bring back the other half by duplicating the existing half.
most face modeling and stuff with matching sides are always best to work on one half cause u will just duplcate the other when ure done.