Ceuta and Melilla, the parts of Spain in Africa, are not external territories. They are an ordinary part of Spain. I say this having visited Ceuta myself recently.
French overseas departments are excluded in the instructions. But I see your point! Ceuta is 17 km/12 miles from the Spanish mainland, compared with 6531 km/4058 miles from metropolitan France to French Guiana. But is it arbitrary to exclude one and include the other anyway? Please give me your feedback, and I'll run with the majority view here.
French overseas department should be included. They are just as part of France as departments in mainland France. Plus, it would be more difficult and thus more interesting if overseas territories were included.