JavaScript, return promise inside arrow function

I've just seen this code:

const buildSW = () => {
  // This will return a Promise <- that comment was present on the code
  workboxBuild
    .injectManifest({
      swSrc: 'src/sw.js'
      // some code
    })
    .then(({ count, size, warnings }) => {
      // some code
    })
    .catch(console.error);
};
buildSW();

The code seems to be working, has been in production like 1 year, but I get confused with the comment of This will return a Promise because I don't see that there is actually a return statement, and the whole code is inside { }.

Shouldn't be?:

return workboxBuild
    .injectManifest({ ...etc

The code is part from this guides:

https://developers.google.com/web/tools/workbox/guides/generate-service-worker/workbox-build

where the return promise is present there. So how or why is working without return in the code showed above?

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