If you resize an image within the article, then all the images will pop-up with that particular article.
However, if in another article, you do not resize any images, then no pop-up will appear. Which is great because it means you have more control over which images you want as a gallery.
The developer should provide some documentation and images, to show exactly how to plugin should be installed, set-up properly and to show how one should edit the images.
Other than the above point (which is immaterial) this is a great plugin. Thanks a million.