It depends on whether Sam is a member of the Kingsguard or simply a skilled warrior in service to the king.
Either way Sam's response depends on how you believe he will act during the feast. Maybe he is trying to outwardly demonstrate that he is enjoying the feast but is internally struggling to control his killing urge.
Maybe it had been a while since he killed and he has been going through a heavy withdrawal. He continues to struggle as the fight between Cleo and Hero begins.
Finally as the feast ends, the king secretlyy calls Sam to his side. He tells Sam to tag along with Cleo and Hero. As soon as they arrest the slaver, he wants Sam to kill him and make it very obvious that the slaver died from the King's justice to the townfolk. He wants to invoke memories of what happened at the village of Rung with this execution. If they fail to arrest the slaver, Sam is to take whatever is necessary to eliminate the slaver.
The King's goal is to brutally and forcefully remind people of what happens to those who don't comply with justice, and to demonstrate to the Kingsguard's two newest members what they are expected to do.
That is how I see it anyway. Kingsguard or not, I see Sam as the King's personal hitman.
