the french changed the latin "super" into sur, while the spanish changed it to "sobre" For south, some vernacular latin word was adopted, because Latin uses "australius" for south. This word was changed by the two into different words, probably gradually

yes c'est tres tres normal

things like that happen all the time, you know. i think it's just a coincidence, a result of some different phonetic processes. anyway, 'south' is SUD in french.