Well, although usually it's a good idea to read the original post first, in this instance the original post is at best misleading because it refers to Plasma as an "operating system" rather than a desktop environment.

(Or for those who want to use even more precise terminology: its full name is either "Plasma Desktop" or "KDE Plasma Desktop", because KDE also has some non-desktop environments such as Plasma Mobile and Plasma Bigscreen... none of which are as popular as Plasma Desktop, though, so usually Plasma Desktop is colloquially called just "Plasma".)