The main differentiator between the two is Inversion of Control.
React developers write their code to be called by the React application. You aren't choosing to include React or not (what you would do with a library), your whole frontend application is built within the context of the React environment in which it will run.
That sounds nice but it’s not that simple. In the case of react you are doing both. You are importing functions like hooks and render. Then you pass render a function that then gets called by react.
The main differentiator between the two is Inversion of Control.
React developers write their code to be called by the React application. You aren't choosing to include React or not (what you would do with a library), your whole frontend application is built within the context of the React environment in which it will run.