At the point of the men demanding some money because their photo was taken, I probably would have handed them a 5 or 10 and hoped it would satisfy them. Telling them to (blank) off was not a very smart thing to do, and just begged for trouble.
Actually, if I had a short lens with me and thought the sign was funny, I may have approached the men telling them I found humor in their sign, and asked if I could take their photo.
That is how I would have handled it. I would have approached him and said "I really like your sign and thing it is funny. I'll give you $5 if you let me take your pic?" Or simple not interact or take his picture and move on. This situation was totally avoidable.
Be that as it may, the fault for the death is still with the person that took a knife and slashed someone.
As for the person that got slashed, it doesn't who is to blame, sadly she learned an expensive lesson.
She did not learn any lesson.
Call it manslaughter or murder or something else, but it seems difficult to justify losing one's life in these circumstances.