It can write a chess engine because it has read the code of a thousand of chess engines. This benchmark measures a different aspect of intelligence.
And as a poker player, I can say that this game is much more challenging for computers than chess, writing a program that can play poker really well and efficiently is an unsolved problem.
Pluribus didn't solve poker. It's limited to fixed starting stack sizes. It can't exploit weak opponents, it tries to approach a Nash equilibrium, but in multiplayer poker, Nash equilibrium doesn't have the theoretical guarantees it does in head's up. And lastly, it requires a ton of compute.
And as a poker player, I can say that this game is much more challenging for computers than chess, writing a program that can play poker really well and efficiently is an unsolved problem.