I am not saying this is the case here. I don't know DHH much, and I don't really care for the whole situation. But using and fronting 'openness' (especially around the 'no-politics', which is political, thing) is a typical way to create non-mixed, non-open community.
The idea is you claim to be open to everyone. This includes people who are judged to be undesirable elsewhere. In fact, you make sure those people want to join by specifically targeting and vilifying specific organization (in this case, you could say Nix or whoever he is talking about). So, by design, you don't create a mixed community, but one with the specific population that feels rejected by whatever or whoever you are targeting/opposing. Because of this concentration of a specific population, member of the organization you are targeting will not be welcomed (which mean it is not truly open). They are on paper, but nobody wants to be part of a community made in majority by people who dislike you.
Now, all this can be used actually for good, for example to create community for the oppressed marginalized or whatever. But it can also very easily be turned into a fascist utopia. It alls come to how you set the rules and how you enforce them within the community, and also simply the people that you are trying to group up. Trying to create a community for disabled people to push for more accessibility within free-software is laudable. Trying to group up people who thinks X or Y are 'clown' usually only lead to the creation of negativity-focused/ego-driven communities.
EDIT: Also, and this is more my (very subjective) opinion, but people who are fronting 'no-politics', 'openness' with no clear claim that whoever they are pointing to are not open, and typically talk about free-speech (not the case here), are typically PoS with big egos who got rejected from the main communities for being PoS and now want to create their own PoS community. See also twitter
EDIT2: Actually, an easy example of this is with reddit. There is often subreddit that I created in reaction of moderation and people being ban from main subreddit X or Y. If you go and look at those communities, they are usually not of very high quality, even more trigger happy on the ban hammer, and have a single focus on what got them ban from the main subreddit in the first place. A very easy example is r/europe vs r/europe_sub. The latter being extremely, if not entirely focused on immigration and being borderline or openly racist.