If you read the replies you can see one from @TonyAlbrecht [1] that states it was implemented, and it was pretty good at the time.
That said all the programs that used design patterns always seemed too synthetic for me, as if the main purpose of the programs were generality. I learned that often it is better to keep other goals in mind, like practicality, simplicity or maintainability.
"Finally reading Design Patterns. The cross platform WYSIWYG editor used as an example doesn't "smell" like something actually implemented."
https://twitter.com/ID_AA_Carmack/status/257683318907215873
I had the same impression. How to trust the authors with such unbelievable example.