It's possible that the value that the Promise rejected with was not an error object, but something else:

(async() => {
  try {
    const result = await Promise.reject(5);
  } catch (error) {
    console.log(error);
    console.log(typeof error);
  }
})();

Doing

throw Error(error);

makes sure that the value being thrown is definitely an Error object, which could be important if the thrown value is examined later and is expected to be such an object. You wouldn't want, for example, for undefined or null to be thrown (strange, I know, but not impossible) and for accessing a property of that to then throw at the point where you're catching for real.

const hello = () => new Promise((resolve, reject) => {
  reject();
});
(async() => {
  try {
    const result = await hello();
  } catch (error) {
    throw error;
  }
})()
  .catch((error) => {
    console.log('The error message was:');
    console.log(error.message);
  });