Cutting a Solid with a sharp edged tool The third point of difference suggests that amorphous solids can't be cut into two parts of regular surfaces 
But glass being an amorphous solid is cut into regular pieces often.
What am I getting wrong?
Your textbook is correct. Glass surface may appear smooth, but in reality it is really rough and irregular if viewed under a microscope. Here you will find some pictures. Have you ever seen an insect walking on a window? It is possible because of those irregularities on the glass surface. Insect legs have tiny hooks which graple to all these lumps, cracks and holes on the glass.