Hi.
I'm not the maintainer, but maybe you'll allow me to comment on your report.
In Debian, I'm afraid the user doing the install of packages is not a notion that we have : packages are always installed by the administrator, i.e. root.
So there's usually no way in such kind of packages to do the work of adding the proper users to the right group.
This is usually documented in the /usr/share/doc/PACKAGE/README.Debian, when additional such steps are required.
In this case, the README isn't very explicit, maybe (and may contain errors, btw), but suggests such adduser commands.
I'd suggest to close the bug, then.
Hope this helps.
Best regards,