After you click on one of them, if you notice, they have the caption on the lightbox slideshow. Thing is, I don’t know how to change the title of the caption as it looks like an event thing? (see blue highlighted)
In the original template code, the captions are hard-coded as h3 elements in the index.html file.
Then, in the main.js file there’s a call to the poptrox function with some code to set the caption text to the text of the h3 element.
You’ll probably need to read the documentation for the poptrox plug-in to figure out how to adapt that to your code.