I'm really excited for you that you have discovered the Son-Rise Program. As a Son-Rise Program Mum who has run a program for 2 years, I would wholeheartedly encourage you to read some of the books recommended on the website and arrange a free phone call with one of the Son-Rise Program family counsellors to help you decide if this is the right program to help your grandson.
The activities you describe are things that a child can do alone, but they can also be made interactive if you approach them differently. If he is routinely playing by himself, you could offer to play with him, supplying the pieces for his shape sorter/puzzle one by one, encouraging him to make eye contact with you by holding them 2 inches in front of the bridge of your nose. Give him lots of praise if he looks, however briefly, but don't with-hold the shape when he doesn't look. Be really excited and enthusiastic about his activity.
If he doesn't want you to join in his game, get your own shape sorter (it doesn't have to be identical) and show him how interested you are in what he is doing by doing the same activity alongside him.
By "joining" him repeatedly, you can begin to build connection. Son-rise also teaches techniques which will help with developing speech and helping the child find the motivation for communicating with language.
I strongly recommend you have a good look round the web-site - there is so much wonderful help there to get you started.
The Son-rise Program has been a life-line to me and my family, and to many others. My advice would be not to wait for a diagnosis, but to try out some of the techniques and see if you see results. One thing is for sure, you will do no harm by trying!