Not "entirely alien, had some ties" is not it. They were part of the same cultural cluster, participated in the same games, traveled to the same sanctuaries, had mutual proxenies. The very fact that we know the opinions of several Athenians about Spartans is telling. We don't know what they thought of inhabitants of Celtic population centers, or Assyrian cities, or Egyptian ones. But we know what they thought of individual Spartans that they mention by name, biographical detail and genealogy.