Yes but the article is specially calling out that using an undo tree is something no one wants.
And that you still want a linear path through your undos and redos...and that's something that Emacs does.
It's more of an implementation detail that is available to users. The article's simplification is also available via :earlier and :later, with the added bonus that they can take _time_ as a parameter as well as a simple revision count. “:earlier 1h” has been handy more than once.