I believe that opinion is shared by Gail Damerow in The Chicken Health Handbook.
If I’m not mistaken, this all began with the gentleman at the hatchery wanting to give you something, when he didn’t feel he had enough chickstarter to share. I think he felt bad about that and tried to make some kind of amends by offering something he could. It wasn’t that he meant to dupe anyone, he just wanted to do something and surely could not foresee the unfortunate result. (It’s not been suggested anywhere here that was his intent, I’m just trying to get to root cause).
So, it looks like if OP is comfortable, the offending grit could be removed for now. (That said, and so sorry for long post, it MIGHT be nice to know what kind of grit it is, and maybe lesson learned is try to always get things labeled, though I understand in the intensity of that particular moment a label was last thing on anyone’s mind.)