these are just "grit" (freeranging) that is not suitable or unnecessary 9wrong size or too many for instance)and the bird has passed them... nothing to worry about.
some how one of my girls got ahold of little bits of glass !! and when she pooped out came the glass ! she had to poop right near me to gross
but that was almost a month ago and she is fine - nothing wrong with her I was worried that the glass would cut her up on its way out but these pieces were really small