> Do we indicate if the backup has been anonymized? Or is that something separate?

It gets printed as a warning to the console when you create the archive:

"Warning: this backup has been anonymised and should NOT be used as a backup. It does NOT contain your data."

But I agree that we should also add that to the archive meta data here.
In fact: I'll take a look to see if its possible/feasible to include the entire log/output in the archive (or otherwise at least all error/warning messages).