Good point. It isn’t variable data as in it only changes on package updates. But it isn’t user data either, so it doesn’t belong in /usr. I guess that one should have been in /lib/share and /lib/man. Or it could be a brand new directory called /doc which contains the documentation type content.
/usr/lib contents belongs in /lib if the contents is installed by the package manager. That way /usr/lib is what the user installed.