Those instructions are making use of the fact that Apple does not immediately disable old OS versions. If you do want to reinstall 8.1.3, without jailbreaking, you would need to do that very soon. Otherwise, Apple will stop validating the downloads and you will be stuck on 8.2.
I had originally planned to keep my iPhone 5C on 7.1. But I am a developer and was having some trouble with an app not running on 7.1 so I went ahead and updated. That was a mistake. 8.1 runs OK, but with noticeably reduced performance and higher memory usage. Unless you truly, sincerely NEED to update your iOS device, my advice is don't do it.