They spent eight hours on one stand? I'm surprised the deer came back! One would think they left a lot of scent around that area.
Is it common to share stands on that lease? If he didn't know where they were hunting, was there some way for him to know it was "the" stand? Was his name on the stand?
Not enough information here for me to decide that the guy was wrong.
Last season, I had a big main frame ten point with a drop tine in my hunting area. Had him under my stand, but no shot. A friend shot him during shotgun season. I was disappointed that I didn't get him, but I sure didn't blame the other guy for taking him. Not exactly the same situation, but my point is as long as another hunter has the right to be there, him getting the deer is just the way it goes. If they guy wanted the buck for his son, he shouldn't have advertised him, especially on land shared with others.