I strongly suspect she's the cause of the problem here.
I think he called her out on having too many items in the express lane and she made it personal instead.
He should not have "called her out". It was none of his business.
What? It's none of his business that he has been inconvenienced by somebody breaking the rules?
A few months ago I was in a Costco parking lot, at an extremely busy time, and I saw somebody loading their car. As is the normal thing to do, I put on my indicator light, signalling to other drivers I was waiting for this car to leave.
As the person drove out, another car swooped into the spot, despite my having waited for it. I'm not normally a confrontational person, but I got out of my car and told the swooper "I was waiting for that spot".
Are you saying people shouldn't be called out for violations of common courtesy and simply get away with them every time?