Compare the questions and the answers.
In the first one, the OP has already installed a secondary desktop and is confused by how that works vs how he expected that to work. Vanadium does a good job at explaining how he can switch desktops.
In the other question the OP clearly shows he understands the concept of a DE and how it works. He is asking if problems could affect his current working DE. And the answer there addresses precisely that.
The questions are phrased very differently and the answers are both specific to their questions.
Perhaps this is a better duplicate: Switching window manager/desktop environments?
What to do?
Personally I'd like if Vanadium's answer could be accepted somehow.
I don't know how vote to reopen or if I need some amount of rep.