It's a rough estimation technique. If every choice/factor divides the number of candidates in half (on average), you can choose between 2^N candidates with N yes/no questions (on average).
I'd assume that they are estimate that 1/8 of the human population plays chess, which feels like an over-estimate to me (but not absurdly, depending on your threshold of "plays"; by a similar process I'd estimate that at least 1/8 of humans alive are under 10 years old).
That's why I said at least 3 bits. If chess players are rarer, then knowing someone is a chess player is a stronger filter. (By the same token, knowing that they're not is a weaker one; but that's not the case we're discussing.)
I'd assume that they are estimate that 1/8 of the human population plays chess, which feels like an over-estimate to me (but not absurdly, depending on your threshold of "plays"; by a similar process I'd estimate that at least 1/8 of humans alive are under 10 years old).