They address this a bit in the article, the hypothesis being that such a simple thing is a litmus test for whether someone is a shitty person in other aspects of life.
Getting angry over this and even discussing it on the internet requires more energy than simply returning the cart.
Returning the cart is good for everyone. Additionally it's a simple contract - if you don't want to return the cart don't take it in the first place.
This is only required where there is a reasonable expectation of privacy, which there certainly is not in a grocery store parking lot.
Given that there are literally cameras everywhere now (including all the Tesla's in the parking lot, with their cams), that's kind of an odd thing to be upset about at this point.
I remember back in the 80s/90s Candid Camera and Cops used to get people to sign a waiver, and those that didn’t had their faces pixelated out.
If all he wants is to be the cart narc and scold people he could do it without the camera.