The difference between rocks and humans(or any living creature) is rather obvious. a tiny stream of balefire can hit a living person and their entire being vanishes into motes and echoes. a nonliving object only gets destroyed where the balefire actually touches it. That's why there are balefire gouges torn out of the hallways of the Andor palace, where as the people dissolve entirely no mater how much, or where, they are hit with the weave.