Why does the “prettyPhoto” plugin open a photo and not a Popup?

Question

JavaScript

There is a gallery page . Powered by Wordpress. The gallery was created using standard WP tools.
When you click on a photo, a Popup opens with a photo from the gallery.

But if you open the same page on your smartphone and click on the photo, the image itself opens, not the Popup.
Despite the fact that on the demo page on the smartphone, the gallery opens exactly the same way as on the Desktop.

Why? And how to fix it?

UPD.
Similarly, if you just shrink the browser window.
Small width opens photo file instead of Popup