Confusing documentation about the end event and screenshots/thumbnails and filenames event

[zya]

In the docs there is this section:

---

'end': processing finished

The end event is emitted when processing has finished. Listeners receive ffmpeg standard output and standard error as arguments, except when generating thumbnails (see below), in which case they receive an array of the generated filenames.

ffmpeg('/path/to/file.avi')
  .on('end', function(stdout, stderr) {
    console.log('Transcoding succeeded !');
  });

stdout is empty when the command outputs to a stream. Both stdout and stderr are limited by the stdoutLines option (defaults to 100 lines).

---

The confusion is about the expected behaviour when generating thumbnails. In the examples here, there seems to be an event called filenames which returns you the list of filenames. In this documentation, it is mentioned that the stout and stderr will be replaced with the filenames when generating thumbnails.
I have not been able to replicate this. As in, even in success cases, the callback arguments are not an array of filenames. And in failure cases, we seem to get stout and stderr as expected.
Is this a mistake in documentation? Or am I understanding the expected behaviour wrong?