What? That makes no sense -- scrollbars are there so you can drag them around and scroll, not just to indicate scrollable content. Not at all analogous in this case. The site looks nice overall, but the explicit indicator is bad design regardless.
Historically, at least, that is exactly what the scrollbar indicates, which is why it is either not shown at all, or shown disabled (i.e. visually distinct) if content is not scrollable.