Many of these islands were not inhabited by humans when first encountered by Europeans. Some had been visited by Arab sailors. Surely, the Giant Bird of Madagascar (now extinct) was the Giant Roc of Arabian stories.

The Comoros were part of the Swahili coastal civilisation as can be seen by their version of Swahili which is the local language.

The modern populations of the Seychelles and Mascarenas islands (Reunion and Mauritius) were brought by the Europeans, as slaves and contract laborers.

How far are they African, as opposed to Indian ocean territories? The independent islands are members of the African Union.

Madagascar of course is the exception. It is a broken off piece of Gondwanaland, the former continent that split into Africa, South America, India, Australia and Antarctica. Its people are mostly descendants of Austronesians who came from Borneo in Indonesia. Its animals represent the descendants of those that lived in Africa before the split. Thus it has no modern monkeys but many species of Lemurs, descended from the ancestors of monkeys.