Why is the Sound settings in the guide different from real-life?

I am trying to enable noise cancelling following this guide.

However, I see that the pulseaudio in my Zorin OS Pro is not the same with that in the guide, because at the end of the guide, I am supposed to run pulseaudio -k, but the output suggests that pulseaudio is not even running.

Just like that confusion was not enough, after searching for a fix, I stumbled upon the official Zorin doc on sounds. However, I noticed that the explanation in that doc does not apply to me at all

For example, the doc makes reference to Zorin Menu → Sound & Video →... several times. However, on my own Zorin Pro, I only have Zorin Menu → Sound →...

Also, the Playback section also showcases a UI that I do not have on my Zorin.

My confusion/question is: why the confusion/discrepancies?

This references a Category in the Zorin App Menu. What categories are shown can be determined by how applications and .desktop files for those applications categorize themselves.
Whether it is sound or sound & video or graphics or accessories or utilities - this depends partly on the Application Developer.
The freedesktop specifications outline what categories are standardized or valid.
You can also reconfigure the menu if you want to, using Libremenu or Alacarte to modify the App menu.

But if you are looking for Sound Recorder application; whether it is categorized under Sound or more broadly under Sound & Video will not inhibit you any from finding the app. You also can search in the app menu by typing the name of what you are looking for, causing suggested applications to show up.
In the app menu type sound and all things related to sound will appear.

Had you installed pavucontrol in the previous step?

sudo apt install pavucontrol

Launch the app either from the app menu (You can search with the above tip) or with alt+F2

pavucontrol

then hit enter.

This is not necessarily abnormal. The pulseaudio -k kills pulseaudio if it is running. You need it to fully restart for the changes you made from the guide to take effect.
You can try rebooting your computer to see if the changes you made were helpful to enabling Noise Canceling or not.
Or you can run

pulseaudio -D

You can check pulseaudios status with

pulseaudio --check