based on the documentation of pkgng: https://wiki.freebsd.org/pkgng#Metadata
the +MANIFEST file is a yaml file, however it seems not to be parsed correctly.
Creating a Manifest with a multiline string as comment:
will lead pkg info to print:
Comment : |-
Them manifest is not actually yaml, it used to be at the very early stage but has quickly moved to something else long before 1.0 (this wiki page is outdated sorry)