I'd say that your buddy is wrong, not you! Open lands, are just that, open to the public! First come, claims the spot! If he did not want you to hunt it, he should not have shown the spot to you!
My hunting buddy and I, do most all the work together. From scouting, clearing lanes, building, and placing stands. I know that not all buddies could have this type of arrangement, but at hunting camp, its like "where do you want to hunt tomorrow?" We've each killed nice deer on each others stands, with NO jealousy!
Again, your friend should not expect youNOT to hunt a certain spot on public land!