He's using 'su' to switch to desktopuser, that's not necessarily, and quite likely not, an account with root privileges. 'su' stands for 'switch user', it's not just to become root.
He uses the term “root terminal”, he writes “Start a root terminal (or a normal one and then ‘sudo su’)”, and he says he only has a single user. One will naturally assume the worst, and in spite of repeatedly posting here he hasn’t exactly made much sense about his workflow and needs beyond launching the browser.
