That's a cool method... nice and easy to do!
What they're doing is using scraps of material, rather than cutting strips off one piece. There would be some wastage, but you would weigh that up against the ease of doing it that way I guess.
To create the block the standard way you would cut squares into triangles, then sew them back together. The problem being that when you cut a square into a triangle you end up with a bias edge (diagonal cut across the grain) which can distort very easily. Half square triangles have to be handled carefully to retain their shape.
Have you had a look at a disappearing nine patch block? That's a really awesome look and a very simple technique, especially for a first.
:-)