That the identification of any group of peoples by their dispersion occurs before the description of Babel, and the fact that at Babel the people had a common language; has no bearing on chronology. It only indicates that Genesis was written after the description of the Tower of Babel incident.
Referring to a particular ethnic group by its general locality is not unusual either in the Bible of in everyday life throughout the ages. Consider the following Scriptures and compare those to exerpts from other writings.
Genesis 36:37 And Samlah died, and Saul of Rehoboth by the river reigned in his stead.
The designation Saul of Rehoboth is only added to seperate this Saul from other individuals named Saul.
Joshua 5:4 And this is the cause why Joshua did circumcise: All the people that came out of Egypt, that were males, even all the men of war, died in the wilderness by the way, after they came out of Egypt.
Just as in Genesis 36:37 Joshua refers to all the people who came out of Egypt in an effort to distinguish that particular group as different from those born after leaving Egypt.
in Genesis 10:5 it is simply a designation of certain maritime tribes from other maratime peoples.
Even today we hear people being referred to as African Americans, or Chinese, or any of another group of peoples, by their ethnic origins, instead of given names. Being an African American in no way indicates that that individual ever lived in Africa as distinguished from the ancestory which did.
Hope this helps.