You are misreading this.
As a sysadmin, you would be able to install a "systemwide Perl installation for all users to use" - one that is separate and distinct from the perl that the system uses.
Typically, it would be in some place like /usr/local, and users would *not* have permissions to install CPAN modules into this perl's @INC directories.
But that would not prevent them from installing modules (to use with this systemwide perl) into their home directories.