A typical website design pattern is "large logo, hero graphic, and prominent navigation on the homepage, minimized logo/hero/navigation on secondary pages." But when a site is only one page, that transition gets tricky, because you don't have a page refresh to provide a cover for the transition. The animation between a maximized and minimized view of the logo/nav is a clever—and depending on your perspective, elegant—solution to the problem.
See also: thisisthebrigade.com
And, you know, what Phil said.