Oh, right, I forgot to answer your other question: this thread was started by an 11-12 kyu player lamenting the fact that he’s forced to play against provisional players; the player in question almost exclusively plays automatch; that’s some evidence that the matchmaking system follows the humble rank.
For more evidence, you can start looking in that user’s page and skim through the profiles of the various [?] players they’ve played with, and you should see that very rarely the first ranked automatch game they played was against a 6 kyu, it’s usually against 11-12-13 kyus, in this one case even against an 18 kyu – and considering 6 kyu is literally the most common established rank on OGS, that sounds unlikely if the matchmaking system followed the true 6 kyu rank.
Admittedly I haven’t performed an extensive search, but for now this evidence is convincing enough for me.