The "boolean" type in a debconf template, can have only two values: true and false. The default has been set to something different.
For more information please consult:
The tag is present in Lintian version
That is the most recent version we know about.
We use semantic versions.
The patch number is a commit step indicator relative to the
release tag in our Git
You can find the detection logic for this version at commit ce6249d. For merge requests, please use the latest version in the Lintian check debian/debconf.