Well, this part:
– means exactly that – you don’t have to follow the steps you’ve posted. IF you haven’t changed default firewalld configuration. 
One more note: open ports for transmission are needed so that other clients from the Internet could connect to your client – so that then can receive parts of the downloads that you already have and they don’t.
But such connections (incoming connections) could also be blocked by your Internet provider and/or your home router. So open ports on your computer doesn’t guarantee that other client can connect to yours.
And transmission will work even if nobody able to connect to you, it’ll be just a bit slower to start new downloads, as all the connections would have to be made by your client, not by other clients in the network.
And this part:
– does the same as the steps you’ve posted, but in cli, not in GUI program.
With one exception: author adds port 65432 to be open in addition to default transmission one (which is 51413), but I couldn’t find any reference to transmission using this port, and he doesn’t explain why he does it.