Sylvia blinked at Longstrider's words in surprise and confusion. She asked out loud right after Longstrider mentioned the talks, "Huh? You guys were talking with the cultists?" Did Shortfang mention that before? Sylvia couldn't really remember. Though then again...there was a lot of stuff going on, so of course she was bound to forget something. She felt kind of embarrassed at the fact that she may have forgotten that Shortfang mentioned it to them. 

The cultists were talking to the Sewer Dragons...

She listened to Shortfang as she explained that they needed allies where they can, and how a dead body wasn't exactly proof. After she asked her questions, Sylvia answered her, "Well, my guess is that the cultist is probably dead for the same reason that they're killing the other trogs, who are supposed to be their allies as well. Troglodytes value strength, and they clearly don't have any problems with killing other trogs, so they probably have no problem killing a human cultist ally. Plus, considering what you just said, I wouldn't be surprised if the trog chieftain realized that the cultists were helping the kobolds as well, and decided to have the cultist killed in order to ensure their victory in this war,"