Jack told him about their experience, as Silverwing and his retinues listened with fascination. He didn't tell them about the experience gathering trick by utilizing NPCs though, but even if he did, there was nothing they could do. It was not like there was a way for them to gain command of an army even if they wanted to.
They did express interest in how he managed to join the kingdom faction though, which allowed him to go on that expedition. He simply said that he had done a quest for a duke which impressed him enough that he had received an invite to join the kingdom faction. Hearing that, Silverwing secretly sent messages to his questing teams to search for all quests pertaining to nobles and for them to perform those quests with merit.
