I don't quite get how a framework can be described as "it's a virtual DOM that's fast". I kind of get what they mean, but is there no better term? E.g. "virtual DOM engine", "virtual DOM runtime", "virtual DOM renderer", maybe?
Some non-VDOM JSX libraries like Solid use it as a static analysis target for optimal output.
Some libraries including React use it to target non-browser render targets. Yes, React is designed to render to arbitrary views or even non-views. It’s used for rendering WebGL, native mobile apps, TV interfaces, CLIs, PDFs and probably a lot else.
As far as what’s described here, “that’s fast” is meant as “which is fast”, it’s distinguishing itself from slower VDOMs (such as React, which is exceedingly well engineered but seldom wins performance contests in recent years).