Sibling at in-state school

I was running the numbers on a college’s financial aid calculator, and one of the questions it asked was whether I have a sibling attending a private college. The answer is no - but I do have one at an in-state state school. Given that that’s around $20,000 per year, it seems weird to just discount it. Is the increase in aid when you have siblings in college just for private colleges? If so, why?