That's one of the pros often mentioned about React. In practice, I haven't found it to be true so far. Once you start using React, you'll almost certainly have to use one the Flux implementations. So let's say you use Redux. Suddenly you also have Actions, Reducers and Stores that you have to learn. If you want to use Async Actions (which is very likely in a web application), you'll probably need Redux Thunk, so that's another concept to understand.

Then there's routing, which is not present in the React core, so you'll need a routing library as well. Again your API surface increases.

In the end, if you want to write a larger application with React, you'll often have a similar or even larger API surface than Angular. I can understand that some people prefer the conceptual model of React (with its focus on Components) over that of Angular. The claims about a smaller "API surface" have always felt wrong to me, though.