Just curious, but why are you so sure this kid did not mean to do it? And why do you think that the dad was a non-custodial parent?
I didn't say that he didn't mean to do it at all; it is VERY possible, if not probable, that his action was deliberate. He might just be a brat, after all, and most ASD kids are as capable of being bratty as any other kid.
What I said was that it was also
possible that *if* he is on the spectrum, that he did not understand that the little girl was a person who could be hurt. This particular concept is very hard for a lot of people to understand, but for kids on the spectrum who lack "theory of mind" it is a fairly common problem. They just don't see other people as people unless they know them very well; they perceive them rather the way that you might a doll: as a "thing" rather than a living being who has feelings. Which isn't to say that he did not deliberately hit her, or that he did not deserve to get consequences for doing so, but most parents would impose a different level of punishment for hitting a doll, as opposed to hitting a person. If the child doesn't know the difference, how do you handle such an incident in a public place?
The suspicion that the father might be a non-custodial parent comes from my experience with non-custodial parents of Autistic kids who are verbal. Sometimes they are in denial of what their kids' limitations are, and sometimes they will go off on the kids as if they should know better when the kid doesn't have a clue why he should be sorry about what he did. More commonly, however, IME they tend to be placators in public, which would explain not taking away the basket -- I'd be willing to bet that if the kid is on the spectrum, taking that basket away would have resulted in a knock-down drag-out physical tantrum. IME, non-custodial parents tend to be less likely to wade into those on purpose if they don't want to sour the time that they have with the kid by deliberately provoking a meltdown, even if they know that they probably should.
So yeah, it is entirely possible that the kid is a brat who wanted to act out a scene from TS3, and the Dad is a full-time parent who just blew it, but if there was a disability present, as the OP seemed to think that there was, what I suggested is also a plausible possibility for what happened.
FWIW, as the parent of a child on the spectrum, I would have handed it this way, while keeping a firm grip on my kid's arm: "Ma'am, I am so very sorry; is your little girl OK? Do you want me to go and get a manager to call paramedics and have her checked out?" [Assuming that victim's parent is not raising a stink at this point, I'd turn to my own child ...] "Son, you hit a little girl with that basket, do you realize that? Yes, you did. You hurt a person who is younger and smaller than you are. You need to tell the little girl and her mother that you are are sorry, and we will need to leave the store without buying anything, because you failed to follow the rule about keeping your hands to yourself." [At this point I'd expect a plaintive argument about how he didn't touch her with his hands.] "It doesn't matter, you still hit a little girl even if your hands did not touch her, because your hands are holding the basket that hit her. No, you need to say that you are sorry right now, and don't tell me, tell the girl and her mom. We are not moving until you say you are sorry." (Please note the lack of pronouns when referring to the strangers; that is important for DS, as when he is under stress he cannot keep actors straight if you use pronouns to refer to them.)
Luckily, my son has never been violent, but to this day I try to avoid taking him into hardware stores because he simply cannot resist playing with long objects like pieces of wood, pipe, or curtain rods. He twirls them, and invariably knocks over displays and even inadvertantly hits people -- most often me. He also is a foot taller than I am; I cannot manhandle him out of the store. Our rule for hardware stores (when they are unavoidable) is that his hands must go into his pockets before we enter the store and must stay there until we have left it.