Maybe the novel will shed more light on it, but it's more likely the dragon isles are so named because the Aspects, once empowered, made their base there, rather than that being where they as protodrakes came from.
That is, it's entirely possible they were just born on ancient Kalimdor, fought Galakrond in what became Northrend, and Tyr brought them to what would later be called the Dragon Isles to transform and empower them.