No theory about it. IF (and that must be assumed for purposes of this discussion) he was acting as described.
You slam a person hard enough with any firm object you will injure them. If it somehow seems silly to you that, in this case, we are referring to a grocerey cart, well then substitute another object.
Running down the isle waving a baseball bat. Not specifically trying to hit someone, just running a high speed waving it all over the place. So, he hits someone with that. Do you consider that more, or less injurious to the person with the cracked wrist?
If you are suggesting that he was not being that aggressive with the cart, that's a different discussion.
As for your reference to the court case, I don't get the connection to this at all.
You seem upset by this one. Wow. Correct me, anyway, but I don't see that this guy actually hurt anyone.
The article doesn't mention any damage. The Zamboni dude got nailed because he slammed the wall. They'd have had a harder time of convicting him if he hadn't hurt any one or thing.
Prosecutors have a hard time convicting drunk bicylists because they can't prove harm. That was why I made the allusion to the recent Scotus case. O'Conner's dissent was based on the notion that the New London case showed no harm done by the landowners whose properties were condemned. In law, or, at least, decent law, harm done is crucial to any guilt.