Kindred & Rift Herald

Aside from me already believing the Herald's stats are too weak for what it gives (Elise can solo it pre-6), I think one thing stands out the most about it: The fact that Mark of the Kindred can proc onto it. I'd like to know why this is a thing, or if it's a bug, since the Rift Herald is supposed to be considered an Epic monster and wolf's portion isn't supposed to be able to mark them.