In the early years of EO uploading through the game didn’t exist and the only way you could upload your scores was manually. Nowadays the game has the option to upload scores automatically, and the need for manual upload became redundant for most people.
This part of the annoucement pertain to people who did use this feature at one point and are looking to save a backup they probably forgot they had.
While it is now possible to upload scores directly from the client, there’s no official way to download those scores back from the site if you ever lost them locally. Hence the notice.