If "they" are not rocks, and "they" are "beings capable of language", shouldn't "chaHbe'" be allowed?
I can see what you are saying, but why would "beings capable of language" be mistaken for rocks. I'm not asking for a creative answer, just pointing out that it would take a rare and unusual circumstance. These is an actual limit to the number of translations allowed, and additionally, if we start imagining wild contexts it's easy for the translations to get to loose and not be helpful in teaching the normal limits of the language. Rocks are not beings capable of language. You are mistaking something for rocks and have to point out that they are not actually rocks. bIH seems like the right pronoun.
I was thinking more figuratively - like - "Those people aren't stupid - they are not rocks", which doesn't seem like a "wild context", but I see your point, and find it reasonable that you wouldn't want to change it.