pkg_info() is a valid ebuild phase. Any eclass can define ${ECLASS}_pkg_info() and call 'EXPORT_FUNCTIONS pkg_info' to export this function to ebuilds inheriting this eclass. (I tested such eclass and it works correctly.) app-vim/gentoo-syntax should support pkg_info argument of EXPORT_FUNCTIONS.
Fixed in git. Going forward, please report bugs via the github repo (https://github.com/gentoo/gentoo-syntax) so they don't get lost here and you can more easily just make pull requests for easy fixes like this.