A previous version of Byobu allowed to create private discussions in arbitrary tags. This is no longer possible in the more recent releases, where private discussions are automatically tag-less and displayed in their own area. The ability to tag private discussions was removed due to the complexity of maintaining the feature.
The recipient editor appearing might be an implementation bug in Byobu. Shadow Hidden discussions count as private discussions in the Flarum API (just like discussions awaiting approval), I assume Byobu forgets to check whether it's a Byobu discussion and just checks whether it's private.