Comment by gwern

That just shows that it worked in some sense. If it didn't reach any ELO, clearly the results would be uninformative: maybe it's impossible to learn chess from PGN, or maybe you just screwed up. He's clear that the point is to interrogate what it learns:

"This model is only trained to predict the next character in PGN strings (1.e4 e5 2.Nf3 …) and is never explicitly given the state of the board or the rules of chess. Despite this, in order to better predict the next character, it learns to compute the state of the board at any point of the game, and learns a diverse set of rules, including check, checkmate, castling, en passant, promotion, pinned pieces, etc. In addition, to better predict the next character it also learns to estimate latent variables such as the ELO rating of the players in the game."