Welcome to WP, I speak for many of us here when I say that your efforts to understand your grandson better are greatly appreciated, and will go a long way towards helping him adapt to the world.
You need to know that you have nothing to feel guilty for. Autism is not caused by the way a child is raised, nor by the physical environment he/she is exposed to (something to remember, as you will come across a lot of bogus research claiming that autism is caused by air, water or ground pollutants, gut bacteria, or vaccines.) Autism is entirely genetic and neurological, and there is nothing you or your grandson's parents could have done to prevent his being autistic.
That said, it's also important to know that autism does not automatically doom a person to an unhappy or inferior life. There are plenty of autistics who are very happy with their lives, not just in spite of their autism, but because of it. Many on this forum are married with children, and are living what people would consider "normal lives". With the right supports, there is no reason your grandson cannot accomplish whatever he wants to.
_________________
"Survival is insufficient" - Seven of Nine
Diagnosed with ASD level 1 on the 10th of April, 2014
Rediagnosed with ASD level 2 on the 4th of May, 2019
Thanks to Olympiadis for my fantastic avatar!