The key phrase in their statement is 'pseudonymous interactions', which is what we have right here. We are not anonymous, because we each have a username and we can develop a rapport of sorts based on who we see around in various threads. What you're thinking of is anonymous interactions, where there's nothing to associate a post to an individual, which are toxic. The surprising thing seen, is that tying your real name to your post actually leads to less civil interactions than pseudonymous nicknames, with the possibility that people are less civil because they're effectively playing it up for their social circle. [Source]:

We built a data set of 45 million comments on news articles on the Huffington Post website between January 2013 and February 2015. During this period, the site moved from a regime of easy anonymity to registered pseudonyms and finally to outsourcing their comments to Facebook. This created three distinct phases.

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We looked initially at the use of swear words and offensive terms – a crude measure of civility. We found that after the first change the use of these words dropped significantly. This was not just because some of the worst offenders left the site. Among those who stayed, language was cleaner after the change than before.

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Our results suggest that the quality of comments was highest in the middle phase. There was a great improvement after the shift from easy or disposable anonymity to what we call “durable pseudonyms”. But instead of improving further after the shift to the real-name phase, the quality of comments actually got worse – not as bad as in the first phase, but still worse by our measure.

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What matters, it seems, is not so much whether you are commenting anonymously, but whether you are invested in your persona and accountable for its behaviour in that particular forum. There seems to be value in enabling people to speak on forums without their comments being connected, via their real names, to other contexts. The online comment management company Disqus, in a similar vein, found that comments made under conditions of durable pseudonymity were rated by other users as having the highest quality.