Those are pretty, and good representational shadows Raptori, but I'm going to argue against them being more realistic. Look outside on a sunny day, shadows cast by most objects are actually quite sharp, and unless there is a second light source, or a highly reflective area behind the object they don't typically fade that visibly unless they are very large objects. That said I think its more important that you shadows look good than are realistic, and your fading shadows pass that test with flying colors.
I think for the brushes he simply means take a brush and paint your own shadow under it, its a great technique and on a couple or rocks like you have very quick. He can correct me if I'm making a poor assumption there.