The problem is confusing. You are looking out on different sides of the graveyard, so you know there is no overlap in statues, and the caretaker informs you tha

The problem is confusing. You are looking out on different sides of the graveyard, so you know there is no overlap in statues, and the caretaker informs you that the total number of statues is either 18 or 20. So you know your friend can only see either 6 or 8. I agree it's not super well-phrased though.