I don't have any proof and if I knew where to get it I would supply it, but reddit's porn scene is huge. There are almost 5m people just on /r/gonewild
https://anvaka.github.io/map-of-reddit/?x=18239&y=12514&z=46...
Which as a url, doesn't necessarily trigger corporate or school blocks unless the gateway is whack-a-mole filtering on subreddit names as well, and I suspect quite a few of those are designed not to reveal the nature of the content through the name alone.
Map is generated by clustering subreddits based on users who comment across subreddits, so I don't think you can infer much from the colored area. That's just background for each group of the graph.