Not entirely true. A package manager is just software that manages software. It can be GUI or CLI. Some GUIs are just front ends to CLI tools and some directly call the associated APIs. ArchLinux is a good example of my point as, by default, Arch just installs a CLI package manager (pacman), but you can install various front ends to it. Mint has CLI package managers too (apt-get, aptitude, etc).
While we're on the topic (and I'm not aiming this specifically at you) I have noticed that there are two popular misconceptions Windows users make about Linux in terms of the CLI/GUI relationship:
- The CLI (Bash, Sh, etc) is the kernel. I can only assume this comes from the Win95 days where you needed the CLI (DOS) to boot Windows. The reality is both the CLI and the GUI are just shells - albeit shells with a very different interface)
- You need the CLI to fix things / some tools doesn't have a GUI. This is usually believed because forums (et al) post CLI instructions to fix faults. However the reason geeks like myself post CLI tools is because it's easier to fix things over the internet via command line tools (I don't need to see what you're seeing to make sure you're clicking the right things, i can just ask you to copy and paste text into a terminal. I also don't need to know what version nor distro you're running as CLI tools are -generally- more consistent between different Linuxes and even UNIX where as the GUI can change wildly from distro to distro and even from desktop to desktop on the same distro where users have customised their install). In almost all cases, there will be GUI tools, but it's just more painful talking someone around a GUI (believe me, I've been there many times! )