Contrast is a point of interest to our eye. In hair color when you have bright highlights next to darker uncolored hair, the bright pieces pop out making the other pieces appear thinner and almost non existant. By filling in the gaps in the color, you can make someones hair appear much longer. For a little added length, stylist Anh Co Tran put in a few pieces of extensions. See his work here
The dark hair underneath is masked by the bright overlying hair. At fist glace all we see is the blonde hair that ends at her collar bone. By brightening all of the hair underneath, it appears much longer.
There is a big gap around her face in this photo which I’ve outlined. The contrast makes the hair appear very fine around her face, really it’s just misplaced highlights. With the proper highlight placement you can see that the hair around her face is quite full.