He provoked Rosenbaum by putting out the arson fire. I would consider the arson fire itself to be the provoking act, though certainly the prosecutor saw this more like he was just minding his own business setting arson fire. But then, the jury didn’t buy that.
As far as Huber or Grosskreutz reasonably believing that Kyle was an active shooter, even if that were true then it might be something that they could use in their own self defense if they had shot Kyle. That did not create an obligation in Kyle, who was not an active shooter, to allow himself to be killed. The question for the jury was if Kyle reasonably believed he was threatened. They answered that question.
Given that he … an overtly armed individual … was attacked, why on earth would you think Rosenbaum wouldn’t have attack him had he been unarmed? Obviously, Rosenbaum was not the least bit intimidated by the gun when he set out after Rittenhouse for putting out his fire.
With the attitude of the man who was killed, more than likely that incident would have still ended in someone being killed had the man who shot him not had a gun.