In Finland you can get out of the game for fighting so his gut reaction might also be that he has to avoid fights if he wants to stay on the ice and keep his top-6 place. He flashed some aggression in the national team, but it's rare and like you said it obviously isn't in his DNA. But if it really comes to it I believe he'll go for it like he did in the AHL.
Well, and to be frank... He didn't do anything remotely worth such a reaction.
If Jesse could add some aggression to his game, he'd be an absolute force in this league. I don't think he's got that in him though, I see him having the potential for Johan Franzen physicality though; where he's not really a physical force, and then just every one and a while the moon aligns and out of nowhere his size just takes over a game.