It's interesting that they can narrow me down to less than 0.1% with just my language list (en-US,en,fr,ro). My user agent is practically unique as well, since I'm running an unusual configuration. I've never thought of that as a disadvantage when it comes to tracking, hah.
I observed this too, but I cannot really believe it. For me it finds just german on the iphone. I get 0.88% for it. But if all Apples do it the same, I can hardly believe this provides already such selectivity. The problem with such test sites seems to me that only nerds visit them, and therefore the database is small and biased.
I have "prefer English, German as fallback". That alone makes me almost unique as well. Not fully (like your special config :D), but enough that other resist fingerprinting options become meaningless.
They narrowed me down to an order of magnitude less based on just my browser user agent (latest Firefox Android). I'm not sure what that actually means.
I like this site for the info on how tracking is done it provides but the data set it generates uniqueness from is really tiny and differs a lot from real world browser makeup.
For instance it claims iOS is 4.63% of users and Safari is 3,42% when all other more complete statistical sources put those numbers at closer to 20%-30%.