Any reasonable reader will assume that the Moon has to fill a significant portion of the frame and be well exposed as well as sharp for this headline to be meaningful.

I agree it’s not precise and I also agree it’s not a generally very useful way to talk about resolution, but I think the authors were looking for a way to convey high resolution and quality while using terms anyone might have heard and have a rough understanding of.

It doesn’t denote quality but quality is the connotation.

In my interpretation, it indicates that the picture contains at least 4000 pixels belonging to the moon.