Technically in React, the reactive callback is still the event handler. It's a two-step process where your event handler is evaluated first, then re-evaluates the component tree which changed as a result of the handler. In your JSFiddle example, if you modify `onChange` to print a console log instead of setting state, you'll see that it doesn't run the component function again.
So really, the key difference between React and Vue is that your function component is not the setup, it's the template.