Hulk anger triggers on other-character damage

Several times, I've seen Hulk Indestructible's black "anger" power trigger when damage is done to a not-Hulk character.  Most recent example is today's Deadpool Daily wave where Hulk arrived upon the death of Bullseye (killed by Chavez "Fear Not" .  Despite Bullseye being the one who took the damage, Hulk's anger power triggered.  Here is a link to a screenshot of full-health hulk with 2 anger tiles on the board.