That doesn't mean much. People wear masks, self-censor or adopt more obtuse language. For example despite using a throwaway right now I am still phrasing things not quite as I would like out of concern that I would not be taken seriously.

"hate speech communities" still consist of people. Those people can engage in other hobbies without injecting their political views into everything. Similar how vegans and meat-eaters can dine in the same establishment and atheists and christians can be buried on the same cemeteries.

I would even argue that dedicated places for hatespeech lead to exaggerated expression of mostly reasonable people. Think of trump promising the wall. People cheered him on for that. But that doesn't really mean they want a wall. They might be perfectly happy with stricter immigration policy or enforcement of existing immigration laws too. But shouting "build the wall" is a group ritual for them. Virtue signalling works for both sides.

Edit: After skimming the paper I noticed that the authors were also identifying subreddit-specific lingo. I wouldn't expect this to carry over unmodified to other subreddits. You can still denigrate particular groups without using those particular keywords.