The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
The upstream source contains a .bzr directory. It was most likely included by accident since bazaar-ng version control directories usually don't belong in releases and may contain the entire repository. When packaging a bzr snapshot, use bzr export to create a clean tree. If an upstream release tarball contains .bzr directories, you should usually report this as a bug upstream.