It always was. Also Indonesia and Japan, etc.
The term Asia has always included the isles off the continent.
The US Fleet stationed at Subic and Manila bay in the 1910s-1941 was the “Asiatic Fleet”.
Guess I’m not old enough. That has been the Pacific fleet during my lifetime.
And the Islands were part of Oceania when I was in the Philippines.
Perhaps a change driven by more refined identification of tectonic plates.