There are too many ways to list, on creating a pop up gallery and is more down to a users choice, hopefully if you can find the solution to the first image missing from the help already provided, you've really answered this question yourself with how you've done it already.
Another way would be to link to 1 image on the Learn More hyperlink already added to the template (just change it from the page link to an image link, you do not need to add hotspots, the link is already there if you open the objects tab and find the correct quickshape within the slider panel) and when choosing the image, select the target window of lightbox and also choose a slideshow name, for example gallery1
Next add more images associated with this gallery and add them to the page, resizing them to be very small and sit just above one of the boxes making sure they sit outside of the slider panel and not sit within it.
Select each image in turn and choose
hyperlink > picture and then again choose the target window of lightbox and select the same gallery slide show name you gave the first image, repeat the same procedure for all the other images associated with this first box.
Finally, we need to hide the images we have above the boxes so they don't show on the page and only get called once the main hyperlink of Learn More is clicked, to do this, right click each image and choose HTML source, then scroll across to the right under the Preamble code for the image and locate the
/*Add Style*/ code, place your cursor before the first / of this code and copy and paste this code
If done correctly, your code will then look like this
Repeat the same procedure for each of the other images on the page, although you can see them in the work window whilst editing, when you preview in a browser or publish to the web, these images will not show and will only be seen when you call the first image from the Learn More text and because all the images associated with the first image are all linked to the same slide show name, you end up with multiple images called to a gallery and lightbox on a single click of an hyperlink.
Repeat again for your next box and images giving the lightbox slide show name another name other than what you used for the first gallery.
To see the above recipe in action using the Pictora Template, check my Demo Here only the first 3 boxes of Landscapes, Cars, Bikes have been configured to use a popup gallery, the last one of Lifestyle is still linked to its original template default of a page (lifestyle.html)
Let us know if that helps