Gallery Filters, how to use in this example?

Please have a look at Gallery in the following example?

http://ift.tt/2fKgegc

I want to adapt this template for my website, however I cannot for the life of me figure out how the gallery filters works. There is no page reloading/php on clicking the filters, and none of the pictures have special tags. If I rename the picture filename it no longer works, so it must use that somehow however I can't find the filenames listed in another file (JS, CSS).

Anyone have any insight on this?