> The right answer is no rocks.

Sand is considered a "rock". If you live in e.g. the USA or the EU you've definitely inadvertently eaten rocks from food produce that's regulated and considered perfectly safe to eat.

It's impossible to completely eliminate such trace contaminants from produce.

Pedantic? Yes, but you also can't expect a machine to confidently give you absolutes is response to questions that don't even warrant them, or to distinguish them from questions like "do mammals lay eggs?".