Lyndaj - your description of your grandson could be a thumbnail of my daughter at the same age. As mentioned, she remained un-diagnosed throughout school and did exceptionally well academically (tho bailed out at tertiary level as she could not handle the social aspects and changed structuring).
School bored her due to the repetition of points she had understood on the first run through, but she was not disruptive and forged ahead by reading the textbooks - usually at the back of the class. It sounds as though your DG is equally bright, and may be well liked by teachers
My daughter was bullied, but mainly because she has very red hair not because of social skills!!
Oddly, she found junior school much harder than secondary level where she discovered more children who were both bright and not popular, with whom she could form a circle of her own.
I would be very reassured, and as others have said, work with educating yourself. As a tip .... the best way to handle is with clear concise instructions given one at a time!! My daughter explains that her wiring is different (and research has indeed shown the brain firing differently) and therefore she cannot "read" facial expressions or intuit what is meant when sentences have more than one meaning..... she asks that people say exactly what they mean. An instance would be : could you do the washing up? to DD, this is not a request, she hears it as "are you able to do washing up", answers in the affirmative and carries on with whatever she is doing blithely unaware that anything was required of her. Distraction (sudden total engagement with something) totally over-rides any earlier directive, so "put away your toys" often resulted in compliance only up to the point that any one toy caught interest. There is no awareness whatsoever that this is not appropriate behaviour and they cannot process the emotional reasons/reactions of those who then become cross. Again, they are mystified by the responses.
It may or may not be of help to you, but if your DGS is anything like my DD then he will slowly learn to read his parents emotive responses simply because of the repetition over years. Not well, but enough to know how to stay within their boundaries. If an action consistent provokes shouting (and loud noise is usually abhorrent) then they do learn where the parental limit lies. It won't always help (we had some major confrontations -particularly in teen years) but it is those very normal responses that DD considers have enabled her to function as well as she does - as I said before.
I think I am wittering on, so will stop, but am very happy to talk through any other experiences of raising a child with this level of ASD if you would like to PM..
Your DGS already has the best thing in the world going for him ....someone who is prepared to understand, and learn, albeit in the background :-)
B x