Incense Burner- What killed me exactly?

Today I got killed after I used the item Incense Burner (https://www.wowhead.com/wotlk/item=33774/incense-burner). The Lich King on the entrance of Utgarde Keep got me under his "grasp" and when he pulled me, the 2 valkirs near him (not his guards, the other 2 near) killed me while he talks.

I reached again my corpse from Valgarde Spirit rest and when I ressed, I buffed me up, and got killed instantly without damage when I started the cast of the Incense burner item.

Here the proofs... But the question is: What killed me?

https://imgur.com/a/bs4V6Ad