On skull damage trait triggers on entangled mobs

I was playing against a team with a hero that had a trait that said “15% chance to kill on damage”.
He triggered his bone dragon while the hero (in first spot) was entangled, yet he still killed my first 3 cards.

Except from me being totally unlucky (again), this seems bugged.
I understand the first 2 guys dying from an entangled enemy, as critical hits do some (extra) damage, even when entangled.

But the last attack (on my 3rd guy), was with a 3 skull attack, which did no damage as the mob is entangled.

Bug: The kill on skull damage trait should not trigger when no actual damage is done.

My second issue would be that crit-ing with 0 attack, is still 0 attack. But I’m assuming that’s a design choice, and not a bug.

This has been mentioned before, coincidentally regarding another Hero class trait: