Trevor Harris was in the middle of doing the Bilby Trap quest when he got spotted and attacked by the dog. I know this because Bilby let Shay Zalandre (me) go down into the quest before Trevor Harris finished.
Unfortunately, I didn't see any error message or anything of the like.
Confirmed, happened to me before with another player starting the quest while I was still in the middle of it.
I can confirm this aswell, happened a long time ago to me too and was even reported (//%22http://www.escapefromunderdark.com/forums/showthread.php?t=38462%22) at that time.