As a Drow he is doubly disgraced: enslavement is horrible, but enslavement by his own people is unfathomable. While the Drow guards keep Drow business to themselves, they clearly see Sarith as less than a true Drow now, and mockingly share his story to shame him further: he is accused of murdering another Drow warrior, and is being held at Velkynvelve until he can be shipped to Menzoberranzan for trial and execution. He will go with the next caravan.