Islands is just a catchy name I guess. I always thought the markojs terms for it made sense, but are more technical / less catchy: they called it “full page hydration” -> everything needs to be delivered as js and “component level hydration” -> islands, only specific component sub-trees need to be hydrated.

Then “sub-component level hydration” would be resumability like in qwik where only events and their dependencies get serialised as client js.

Yeah. Well to their defense, it is probably to be understood as islands of interactivity lost in a sea of static elements. The term is definitely more evocative.