Sam didn't know what is happening in the imperial capital, but what he does know is that he was being deliberately targeted by these imperial scions and the team that went to Flavos.
He can take it when they just separate him from their team in the Volcanic region because it is a fact that he is not from the team and he went there individually. He can even take it that they planned to attack him along with the other teams as that is for the treasure and they are still within the volcanic region.
As for the current situation, he wouldn't take it lying down. Barging in and spoiling his dinner might sound small, and his reaction might be exaggerated but he has another hunch and he wants to confirm if it was true.
He wants to see if there is anyone behind this or this is really the action of the stupid prince. He doesn't have any concrete clues or signs to show anyone's involvement, but if there is really one he has to send them a message and that is why he took a hardstand.
