Deep pressure (which is provided by the heavy blanket) is very good for many children, not just autistic children. It works for some kids with sensory integration issues, attention deficit disorder, etc. my son would react very adversely to light touch (as a preemie in the NICU). Lots of kids like the security and feeling/sensory input of a weighted blanket. We even put weighted vests on some kids in the school and it really helps.
I am sure your DGS will love the quilt. Make sure you post pictures.