React is neither MVC or notMVC. It’s a library to render the View (with a lots of cool stuff, but still). You can use either MVC patterns, or Flux/Redux, or whatever.
The difference between MVC and Flux is that latest implements unidirectional data flow. So your data can move only one direction. Action -> Middleware -> Store -> View. MVC is bidirectional; you can change Model from View and from Controller.