"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.
Generally the difference between a library and a framework is that you can use bits and pieces of a library to add functionality to your project.
A framework expects most of your project to be shoehorned into it.
Whether something is one or the other depends on which of the two most users are doing. It's not a very interesting argument, though, because debating semantics is the worst use of the limited time you have on this planet.
I think it's a shortcut for saying that react doesn't have an 'official' routing library (like vue-router) and state management library (like vue's pinia). So depending on what you choose to manage routing / state, one react app can be quite different from another.
Maybe nowadays there is a set of popular libraries for react so it becomes framework-y?