he is used to a routine u have to replace thigs gradually so perhaps make it routine first ure usual shop to town perhaps you both pick up a book tgeva u read it aloud as he spins the glass he may show interest and come to you try engaging ito wat he likes wether it be mario bob the builder and buy that book maybe you cud make a book tgeva from a magazine cutting out pictures of things he likes from argos catelogues or makig ure own story to help engage him in books wud help with pictures as autistic children are visual

I would take him outside to play maybe the park or just a car ride to remove him when hes too fixated.

Your grandson is visually stimming getting eye level watching it spin. My son visually stims off his cars and trains getting to eye level and lining them up or in weird positions. We tried taking the tv and toys away but that just made him stim in other ways especially vocally. We let him do it cause thats what he enjoys but now he moves on to other things and will resort back.

I doubt his mother should take some blame not talking to him or interacting with him at a younger age. The "refrigerator mom" as a source for autism was a popular theory at one time but there was nothing to back it up. A lot of parents dealing with ASD are heavily involved (probably more than ordinary parents) with their kids but it can be slow going.

It's hard to mold some ASD kids. They see other toys but they don't just don't get the same "kick" from them. My daughter threw books in the air and now throws them out the door. She now plays with typical toys in a somewhat typical way but we didn't force her to. Maybe she saw other kids playing and picked it up. It's ok to show your grandson how to play with something correctly but I wouldn't fret if he doesn't.

It probably calms him, the spinning that is.
A lot of autistic children have one kind of play that interests the child.
I wouldn't say you should encourage him to spin but there seems to be no need to take away the spinning play. Remember that he sees the surrounding tho it doesnt seem like it and he e may have hard time expressing himself (imagine how difficult it must be for him as he feels a lot of things but he can't express!) so the spinning could be one thing that relaxes him. Do talk to him while he spins. He may not respond but he hears you and he will hear you even better when this becomes a repeated routine :)