[Inyokern]

I didn't think it was referring to Kedar as an island.

Of course he wasn't. He was referring to several places, Kedar being only one of them. The "Islands" in the Bible usually mean the area of Greece.

This passage in Isaiah refers to Arabia as only one of several places. It does not seem to be a prophecy about Islam.

[Patria One]

Hmmm. Ishmael and the sons of Keturah and Abraham went to Arabia and the Rabbis of the Jewish tribe in Yatrib prophesied about a messenger who would come to the Arabs.