That's because they are using a fixed-height container element with an "overflow: scroll" on it, which is needed to get that little grey bar at the bottom to complete the "page of paper on grey background" feel.

Which of course completely ignores that a page of paper can't scroll, but I guess doing it in a way where the content is split over multiple "pages" underneath each other is too complicated for a basic website - and would be even more jarring to the average reader.