Possibly, but not necessarily, often it's simply a self-selecting group of various levels of ability. The kind of selectivity you describe is a personal choice; it doesn't require a clique to be present. A lot of dancers make those kinds of choices even if they are part of no group at all.
The question is, whether the tango community is a representative subset of our society, or it rather resembles a modern sort of limbo, as seen by the Third Space Theory. I am in two minds. I do recognize all characters I know from the world outside. On the other hand I find that some characters concentrate in our ranks to a greater extend, I mean singles, spiritual people, and also the relational handicapped or burdened. Luckily I must not reduce tango to only one of these assumptions. In practice, there are people at my local milonga I defenitely know nothing about. They blow in ephemerally, and disappear unrecognized. I only know their night face, smell, embrace, body response, alias, nothing else. But there also are dancers I saw at daylight, I regularly meet in the supermarket or railway station. And of course there are additional subsets, for instance dancers I did invite to my birthday parties, or call for having a beer in the afternoon. And there are former dance partners. A permanent dance partner is a special sort of a human being. Its a qualified relationship that comes close to a life partner. The dance partner knows everything of you, he comports you in times of sorrow, and temporarily shelters you.
From what I have scene, it's not, certainly not demographically or economically.
Delicious!
Something exactly like that happened to me twice last year. Needless to say I never danced again with either of these women. One of them went further bringing next milonga a hat of her political X preference so knowledgeable men will not likely approach her.