Hmm, I understand where you are coming from now but when I read your original post I interpreted it this way.

You put him in a stand where there was a big buck running around in the hope that he would get a shot at him. You didn't post, originally, that he wasn't supposed to shoot anything but the big buck. Did you mean to post that but didn't?

If you did tell him to only shoot the big 'un and he shot the little guys then I would be a bit upset as well. I would still let him hunt this year though while giving him explicit instructions to only shoot this or that specific deer or he is just done hunting your property.