href="#"

I've been looking over a web site that pops up a modal box when you click a "Read More" link and then dismisses the box when you click "close" at the top of the box.  The way they do this, though, is strange. No jQuery is involved.  The Read More link initiates a reload of the page with a query string that causes PHP to include extra code just before the </body> tag.  This extra markup includes an "overlay" div with width = height = 100%, color = black, opacity = 0.75, and z-index = 100. After the overlay div comes the pop up box with a z-index of 102.

The thing that puzzles me is the way they close the box. "Close" is just a link with href="#".   Somehow, it seems, this has to reload the original version of the page, that doesn't have the overlay div and box div at the bottom, to make the popup go away, but it's not clear how href="#" does  this. My understanding of href="#" is that it just jumps to the top of the page.

Could anyone explain what's going on here?  You can see the page at www.thebarcoderegistry.com.  Just click any of four Read More links.

Thanks for any insight.