Is this a Mist Walker thing?
Maybe he ran into a pickpocket mine. Pretty sure those do some damage to you as well as the knockback/item drop.
I got some torment debuff once or twice, but I didn’t see any way to apply that via ghost so not sure where it came from. I was literally alone by myself when I got it too.
Torment comes from the ghost’s #3 skill. The beacon trap or something like that.