Is there any relation between the font rendering engine and the font being hinted for Windows? When I saw the title of the article on the page my first thought was the font not being properly hinted for Windows.

You're right, it most likely means font is not hinted for windows. That looks horrible when rendered with GDI at smaller sizes because GDI hammers everything into pixel grid and doesn't do vertical anti-aliasing. DirectWrite features anti-aliasing in both directions and doesn't try to fit everything into pixel grid. Because of that non-hinted fonts look much better, although blurrier, with DW than with GDI.