React elements and fat arrow functions

In the Redux examples, the syntax used is:

const App = () => (
  <div>
    <AddTodo />
    <VisibleTodoList />
    <Footer />
  </div>
)

I was toying around with a new example app and mistyped the above code with curly brackets instead of parentheses like so:

const App = () => {
  <div>
    <AddTodo />
    <VisibleTodoList />
    <Footer />
  </div>
}

I console logged both of the following and the result seemed to be the same. My question is what is the difference between these 2 and why does React like the parentheses but not the curly brackets?