Yes, you need to do that. You have copied your /home files to sda1, so now you need to make a mountpoint named home in the / directory. This command renames the old /home directory to /home_old so that you can make a new directory /home as the mountpoint for your sda1 partition. The old /home directory could have been deleted instead of just renamed here, but it is safer to keep the files in it until you are sure everything is working right, then delete the /home_old and its files in the "Clean Up" step. The syntax of the command is to first change the working directory to /, then if that is successful, rename the /home directory, then if that is successful make the new /home directory.
EDIT: Ignore the above, I misunderstood what you are doing. I just noticed
that you already have a separate partition for home, so what you are doing is different from the instructions you are following. You really just want to change /home from one partition to another, so after moving the files to sda1, you could just modify fstab to mount sda1 to /home instead of sda4, in which case you don't need to do that last step, just modify fstab and reboot.
In theory, theory and practice are the same. In practice, they ain't.