UPDATE: Evidently Hacker News removes the hash appended to the end of a URL so it doesn't go straight to the entry :/

The doc didn't give me a satisfactory answer. This, however, did: https://en.m.wikipedia.org/wiki/Gollum_(software)

One of the cool things with the update adding git support to GitHub Wiki was that it was using gollum (https://github.com/gollum/gollum) and GitHub wanted to become more open source themselves (https://github.blog/2010-08-12-making-github-more-open-git-b...). Sadly, it seems like they have diverged by now, according to the GitHub Wiki on the gollum repository.

Seems there is still some historical artifacts from it left.

It seems a bit unusual that there is an event for when someone creates or updates a wiki page, but no event for when someone deletes a wiki page. So if you want some automation that notifies you about page deletions, it can't be done via the GitHub API.