I think React could be a library if it were only used for HTML rendering. However once you start layering on component-based design, state mgmt and props, JSX, etc., it starts crossing into framework territory.
React can still be used as a library when you use a design pattern like MVU. For example, you can accomplish this with Fable-Elmish. At one point Fable-Elmish had multiple HTML renderers available, including React. (If you can swap it out, that is a good sign.) I think the other renderers are no longer maintained because React exists and does a decent job.
Anyway, I completely agree with K's assessment about framework vs library.
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