You may be missing the point of the statement (or perhaps people are using it wrong?) - but let me give you this example.

Midjourney doesn't understand what a hand is. It knows what one looks like, so it can draw it in most cases. But it has no understanding of it's use in any real sense. That means it will quite happily draw a hand in a position that would break bones and tendons of a human. That's not an issue when you're just doing a drawing, but there are plenty of cases where that lack of context can be an issue. And it may not be just the case of feeding it more data.

That is the kind of understanding that is entirely relevant and not stupid to point out. yes, people get input data to learn, but they also have other senses like pain for instance. They also get experience by trying things out, i.e. experience.

A problem for AI in some tasks is that it has a lack of understanding of the implication of it's choices.