A human wouldn't mindlessly reproduce the signature due to "not reasoning" and being intellectually lazy while doing the drawing. For the human, including the signature is more effort than omitting it; for the generative system, it appears the opposite is true. The point is to highlight that difference.

Is that a useful point though?

It's like accusing somebody of being a lousy chef because they have such terrible taste in takeout. There's just no connection between these things.