You are misunderstanding the post. Thrash, for mobs that have it, is an on-hit ability, NOT a cast that is stored. What’s happening, and happening every single time, is that NPC’s are storing auto attacks x5 when they catch you. If you want actual proof specifically of Princess Theradras NOT behaving that way in classic, look at the 4 videos I just posted, 32 posts down, in this thread Princess Theradras changes, no longer kiteable - #32 by Affix-herod
But as being posted, this problem is happening with a variety of creatures, and more noise will get made as more players are 1-shot randomly in dungeons and raids, like by the time half the raid trash is being kited in BWL?