I am not sure about the other plugins, but this is how it is different from the parent plugin (ref - https://github.com/jbutz/bootstrap-lightbox)

1. The parent plugin could attach to one element through the HTML changes. The JS change - you need to explicitly bind the lightbox to click event. In the current plugin - you do not need to edit any of the existing HTML. Just add one line of JS to view all the images (or probably a select few) in Lightbox on the page.

2. While providing this feature, it might not be evident to the user that clicking on the image shows it inside Lightbox. Hence the tooltip.