Figure 3 is incomplete; as the space depicted in it is not a valid board configuration. If either x or x' is false, then the respective 1s on the extreme sides will be invalid. This is either a crop of a real situation (in which we assume the wire repeats beyond the scope of the image), or an error.
It is a crop of a board containing a wire that extends beyond the area shown. It is not an error, although indicating (somehow - people's intuitions vary) that it's a crop would help.
