Hi, Sabir!
One thing is an Excel file downloadable from a website and other thing is an HTML page at a website. Even in both cases the website is this, chandoo.org, your posted link leads to an article that -sooner or later- it ends in HTML code so as to be accessible from browsers. Nothing Excel related, except the subject and contents. Despite of this, .GIF is a Windows file type for storing images and there's as .ANI known as animated GIF that's neither natively supported by Excel nor other Office product, except PowerPoint.
Hope it helps.
Regards!