asked the mod autor this very question but hhe said its intended

To explain, or at least have my basic grasp, there should be, as a part of their Information tabs, a "toxic sensitivity" on creatures like it. This will tell you how sensitive they are to Toxins - 50% meaning 50% of all toxin damage is taken, 0% means no toxin damage, and 100% (base) is 100% of all toxin damage is taken.

If this number somehow ends up being higher than 100%, then that means one takes (x-100)% more toxin damage. 150% toxin damage makes you take an additional 50% toxin damage.

It could also be a "threshold" resistance or something.