Read the next article Written by Luca for a more in depth look for ReFS integration.
Maybe this was the misinterpreted expected result.
I guess you where looking after "a-few-seconds-later" backup-copy-job succesfull...
but it does not quite function that way you wanted or expected it too, also in regards a "clone" as where you expected ReFS clone-functionality in a "back-up copy job".
Not to be mistaken with thin clone functionality at the storage level in terms of the Back-up copy job wich is a 1:1 relation to the original backup file as well in copied size.http://www.virtualtothecore.com/en/windows-2016-and-storage-spaces-as-a-veeam-backup-repository