The launcher is separate from the update files it downloads to get a specific editor version. The launcher doesn't update itself, you'll need to download and reinstall to do that.
In this case the older launcher didn't know about a command line parameter, even though the newer editor version would have. In that case you can use --ignore-unknown-args (or --unknown) so the launcher won't try to verify the arguments are correct. It will just give them to the editor.
