This may look low: ELO for mediocre players is 1500. But if it is obeying the rules of the game, then this is big. This is a signal that if it learns some expertise, like discovering how to use or create better search algorithms (like MCTS and heuristics to evaluate a state) and improve by itself (somewhat like alphazero did), then it may eventually reach superhuman level.
It may then reach superhuman level in any task simpler than chess which is enough to destroy many human jobs.
EDIT: From the article: "With this prompt ChatGPT almost always plays fully legal games." Relax: we're still far from that.