I don't understand what this is, based on this statement:

"Astro supports every major UI framework. Bring your existing components and take advantage of Astro's optimized client build performance."

But isn't Astro a framework itself? And then apparently you need Node as well. The frameworks upon frameworks in Web development are baffling.

Astro is a meta-framework that allows you to plug in other web frameworks where you need it (React, Solid, etc). Although it would also be fair to consider Astro a sort of build tool / bundler.

Node is a runtime, not a framework.

So there's really only one framework here (Astro). Using other web frameworks within it is completely optional.

It means the island bit where you can mark areas of a page as non static and then run react or other framework as components

Web dev is a royal mess, but what isn't in current times? Too many opinions not enough direction.