One of my pet peeves is when folks compare human elo ratings from FIDE to (presumably) engine elo ratings from CCRL, a league for chess engines. They're not the same! This is like comparing points between your local youth soccer league and La Liga. All we need to say is that this engine is only 100 elo behind Stockfish. That is akin to occasionally beating God in a game of chess.
I agree with what you're saying. On the flip side, there are multiple systems (Elo, Glicko), anchors, playing pools, etc. in use around the place, and FIDE and CCRL are offset by around 80 magnitude I heard, compared to about 600-700 difference between top humans and top engines.
So for a non-technical audience, I feel like it's easier to give a ballpark that they can understand without having to pull in too much context around Stockfish, CCRL, etc. It may have been better to clarify further in the docs though.
The "Data" document does give the relative Elo breakdown in the appendices.
The comparison between SF and AZ is hardware-dependent, so there was never a black-and-white answer. Even so, AZ hasn't seen any further development AFAIK but SF is constantly improving. But for this engine, I'm just relying on the author's methodology:
> It plays chess with a rating of approximately 3450 Elo... [compared to] Stockfish 14 at 3550 Elo.
