Scrolling on that page misbehaves because the images are in a div #contents with overflow-y: scroll, while its parent divs and body have overflow: hidden. Commenting out all the overflow CSS fixes scrolling (but breaks the sticky header and footer).

Hmm, not the creator but the page source looks fine. There's no JS, and the images just have this CSS:

  .scale-img-half {
     width: 46vmin;
     border: 1px solid #404040;
  }

What browser are you using?

scrolling doesn't appear to work at all for me on Chrome 71, macOS

you have to have your mouse over/focus on the main body div, since it appears to be centered and overflow: hidden.