Because he only wants to disable the notifier, not the entire octopi. If he wants to uninstall the entire octopi, then yes, the command he needs to use is sudo pacman -Rs octopi, not -Rsn though. -Rsc if he wants to also remove the packages that depend on the dependencies of octopi.
Remove all target packages, as well as all packages that depend on one or more
target packages. This operation is recursive, and must be used with care since it
can remove many potentially needed packages.
Removes the database entry only. Leaves all files in place.
Instructs pacman to ignore file backup designations. Normally, when a file is
removed from the system the database is checked to see if the file should be
renamed with a ".pacsave" extension.
Remove each target specified including all of their dependencies, provided that
(A) they are not required by other packages; and (B) they were not explicitly
installed by the user. This operation is recursive and analogous to a backwards
--sync operation, and helps keep a clean system without orphans. If you want to
omit condition (B), pass this option twice.
Removes the targets that are not required by any other packages. This is mostly
useful when removing a group without using the -c option, to avoid breaking any