Clark Kent on Smallville was definitely retarded and that's why he couldn't fly even though every other Kryptonian could fly after having spent MINUTES on Earth.
I just think he never even tried. I don't think it would occur to anyone - alien or not - that they could fly.
Except the numerous times he himself flew, including when he woke up floating in the pilot episode, or met Krytponians who could fly.
I read it as Clark IN Smallville as in referring to the movie version. My fault.