I am so confused

Yesterday I had to punish Brian. When I told him the changes what would take place until his grades improved he sat there for a second and then came back with. "Fair enough."
What does that mean?!?!?! I didn't punish him hard enough if he approves? That he would have countered the punishment if he felt it wasn't fair? Or that he honestly think I punish fairly? I felt defeated when he said that like I didn't punish him at all.