"React is actually a library, not a framework" is definitely a thing people have said here and there since its inception. It's a distinction that doesn't seem to buy anything in terms of explanatory power or clarity, so I tend to ignore it.

you can use React like a library, but I have never really seen it done.

Depends on the definition.

jQuery isn’t a “framework” either, at least not like Angular or Vue, though it can be extended with “plugins.”

Both jQuery and React are foundational technologies, so comparison is valid.

jQuery isn’t exactly a “framework” either, at least not like Angular or Vue, though it can be extended with “plugins.”

Both jQuery and React are foundational technologies, and comparison is valid.