Its not a framework because it doesnt encompass all of the tools in a full development environment such as linting for example. Compared to Angular it is absolutely a library.
There is a big difference, and React is meant to be expanded upon by 3rd party libraries to make up a framework.
A library is a packet of functions and components to do a specific job.
A framework is something that is the “whole” of what your project being handled by.
Especially now that you can have private repos for free
Couldn’t have explained it better.