Do you think these people also knew about all the other continents of Earth with other people on them? It seems possible to me it happened on one continent but seems unlikely they really knew about everyone at the time.
Fun question. The people of Cain had cities, Cain was concerned that he would be restless wanderer on the earth with fear of vigilantes. During this time there was a single language, with humans (with very long life spans) filling the earth. Nineveh and Calah were two large cities, further from Eden it would seem, meaning there was sea travel and being pre-flood, the land configuration may have been significantly different.
