The UI may have some wiki-like characteristics, but, when you're talking about the social environment instead of the UI, it's kind of a distinction without a difference.
Example: Wikipedia has similar social problems regarding new contributors.
SE have explicitly stated that the site is a Wiki.
"Stack Overflow ultimately has much more in common with Wikipedia than a discussion forum." Jeff Atwood, "What does Stack Overflow want to be when it grows up?", 22 October 2018.
