Alright so, this may depend specifically on the type of enemy you are facing. But, during my explorations before even going attending Beasts class. I was level 22 facing a level 30 boss. It was the spider in the Forbidden Woods quest.

After several attempts of trying to kill it, i got it down to a quarter to half health. It teleported to me but also landed of top of one of the smaller spiders making it instantly die.

I have a clip of it loaded on my xbox if anyone wants to see it on Demonic5andwich or I can figure out how to upload to youtube again.

This is the video in question: https://gamerdvr.com/gamer/demonic5andwich/video/172371717

enemies have friendly fire, I think it's the other spider killed it. Not sure.

I also came across something similar. I was facing the first infamous foe when you enter the southern region, Poidsear Castle, she let's say 'miswarped' and instead of warping on the ground she was in the air and instantly died when she landed.

So I believe that the warping mechanic the enemies have can instantly kill an enemy if your lucky.

To me it looks like it's related to fall/impact damage