No. It has no visual similarities. Skyloft is green and natural, the City in the Sky is cold and mechanical. Skyloft is held aloft by the goddess, the City in the Sky is held up by propellors. Also, where did the chicken people come from?
I always thought the City in the Sky was Skyloft. Skyloft doesn't look very similer to the City in the Sky during SS, but I always thought that as time went on, that Skyloft evovled through out the years and changed into the fortress that is the City in the Sky.
You might be correct because the skyloftians might have evolved into the Oocas and before they did they made the city better. then the Loftwings might have changed into the badies that fly around and there master is the giant dragon.