Flipping coins, sure. But in that instance it can be in one of three states - being heads or tails when at rest doesn't preclude it from being neither (or both) whilst in motion.
But people (in the context of knowledge as we're discussing) are less like one-state-or-the-other as much as they're zero or non-zero. And if you accept they're either zero or non-zero, that doesn't leave a third alternative.
Of course, this all depends on one's definition of 'know'. For the sake of this argument, I'm using "to have no knowledge of, compared to having some knowledge of".
But people (in the context of knowledge as we're discussing) are less like one-state-or-the-other as much as they're zero or non-zero. And if you accept they're either zero or non-zero, that doesn't leave a third alternative.
Of course, this all depends on one's definition of 'know'. For the sake of this argument, I'm using "to have no knowledge of, compared to having some knowledge of".