React is JavaScript
(this can be done manually, or automated with React or JavaScript)
In the specific case at hand, I believe the author meant ‘vanilla JavaScript’, but it’s too close for comfort to the common belief that React and JavaScript are separate and you learn one or the other. Eric Bailey put it well while talking about Web Components:
We’ve already seem [sic] this phenomenon with libraries and frameworks creating their own markup patterns that are less robust than their native HTML equivalents.
The worst of the problems that arise from this situation is that it teaches people to think and work framework-first. When that happens, the hard-won, baked-in interoperability and, importantly, accessibility of the platform is thrown away. It’s a compounding problem, as well: The more people don’t use the elements made available to us, the more the notion exists that they’re irrelevant
That’s what You might not need JQuery is all about. I’m sure we need something similar for React. Don’t get me wrong, I believe in the power of tools & frameworks—I’m a big fan of Svelte, and this blog is built using 11ty, as just two examples. However, these should be used to alleviate unnecessary tedium and complexity, not to avoid understanding the HTML, CSS, and JavaScript the browser will receive in the end.
Jim Nielsen’s post on Web Languages as Compile Targets is good reading that puts these concerns in context and suggests a way forward.