The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
The package appears to be a release candidate or preview release, but the version sorts higher than the expected final release.
For non-native packages, the check examines the upstream version. For native packages, it looks at the Debian maintainer's revision.
Please refer to Debian Policy Manual section 5.6.12 for details.