This appears to be a mirror of the CORE conference ranking. It's "official" in the sense that it is (if I remember correctly) maintained by a non-profit sponsored by the Australian government and heavily used in Australia. Everywhere else it's just an opinion point, like every other ranking. My impression is that it's one of the more widely accepted conference rankings, but of course there is still plenty to argue about.
Note that having the "one universally accepted ranking" is impossible to achieve. Different researchers value different things, and a conference that may be modestly interesting to one may be of highest quality to the other. Acceptance rates are also a fairly useless metric of assessing competitiveness, as many middling conferences (at least in my field) get overproportionally many terrible papers, which apparently the authors did not even try submitting to the top conferences.