I'm still interested. I leapt on it thinking I'd be hugely reassured but it's more the opposite.
From the OP I'd say an overinflated sense of justice is common in verbally able 4-5 year old children, especially firstborns. It might also be common in less expressive children, they just can't tell us. And playing by himself, or alongside rather than interacting with friends, surely is still in the normal range with a 4 year old. The eye contact might be more of a problem.
My DS is very able in maths but he lacks understanding of language and can struggle with really basic stuff. Yesterday I asked him to bring something from the coffee table and I got lots of aggression and basically snarling from him, because he said he didn't understand. He has derived his own long multiplication methods at age 6 and he doesn't know what a coffee table is. The thing that's been in the middle of our living room for a year. Or he says he doesn't know, anyway. But he reads with nice expression and can be thoughtful. When he has a friend round, he wants to lend them his favourite plate, and he is very affectionate to us on his own terms.
But his play is not like his friends' play. As Shaffron says, we expect children to pretend, to play creatively and draw. He likes to run 4 player monopoly games by himself, or he assembles lego sets strictly from the instructions. No deviation is allowed - if a piece goes missing he will abandon a model he's worked on for hours, he won't accept any substitution unless absolutely identical. He hates to draw because he's always disappointed with the results. He rattles off Strictly stats from last year and got really angry with me today because I couldn't validate his assertion that it snowed on the 2nd Feb. He knows all his classmates' birthdays and who is the 11th oldest girl, etc., and can calculate what day of the week their birthdays are, or were, on. He's been called "Rain Man" more times than I'd like, but I think people mean well.
"Neurotypical" is a funny word. I don't think he is wired quite normally, but we are all different, and someone who can think Y4 maths trivial in Y1 is not thinking "typically". That doesn't mean he has ASD. I think he is just a very "male-brained", very perfectionist, bright child who is not a verbal learner and doesn't respond well to the constant talking everyone else does! I mostly think he can't have ASD, he's in the normal range socially, but every now and again I worry.