If that’s true, it actually seems like a pretty big oversight. The power’s description says “If Black Panther would take [number] or more damage, negate [number]% of that damage and stun him for 2 turns.” It doesn’t say anything about the damage having to be exclusively directed at him.
Yeah, we’ve brought that up before. Nevertheless, it has been stated that it is intentional that he has to be the target of the attack before MoBM will trigger.
Oh yes, of course, worth pointing out it will still sort of work if he’s hit by an AOE stun or random target stun. He’ll take the full damage but will retaliate when the stun ends.