How can you tell? Did you work on it for a few months or you can just browse the SVN and notice it's well designed? I look and all I see at first is indentation style and directory organization.
If all you noticed from seriously looking through the source is that it is well indented and well organized, you're probably not an experienced enough C++ programmer to evaluate the merits (no offense intended).
How can you "infer" the design only by looking at a pile of C++?