Poison bug or not?

Hello. I played classic only a few times and mostly on mid-range servers so i don't know if this is a bug or just a peculiarity of this chronicle. When i was low lvl (9-13) mobs that have poisoning skill hit me with this skill for 600+ dmg. It has chance of success around 80-90% but that classic mechanic i get it. But why dmg is so high?
Now I'm in ant nest and sometimes ants hitting me with poisoning around 1200+! Which is 50% of my hp. Just want to know if it should be like that.

On classic poison may critical damage. This aspect affects all DOT's in-game.

I see. Thanks.