That's not correct. It doesn't matter whether they can explain their moves to you. What matters is if they can explain their moves to another grand master and they always can unless they moved a random piece to break up a position to make a boring game more interesting (this rarely happens, but it is an interesting way to play, but not to win contests).
They are not explaining their internal processes (neurobiology, brain chemistry, neuron firing patterns etc.) that caused them to arrive at given moves. They just provide proofs that their moves were good.
Works for me. Just like you won't be able to explain to a lay person what a computer program does doesn't mean that the logic is sound without going all the way to the atomic level. But if you really wanted to you could because a computer is a deterministic and relatively simple system, small enough to explain in principle from which we can extrapolate. Wetware doesn't have that luxury so you have the choice to believe the explainer, or not. But when dealing with such a vast gap in experience the best way is to try to learn as much as possible from such an explanation in the hope that you'll be able to capture more of it in the future. This isn't always possible, for instance due to time constraints or interest levels but in principle it could be done.
