I agree with you. The victim evidently started things by throwing water. Stupid move on his (her?) part. Although the water injured no one, it was wrong to throw it. And it probably was a criminal offense.
The three girls took that as reason enough to lay down a fatal beating. Who behaves that way? Savages do.
I saw more than one incident like that in my years as an urban public school teacher. Person A does something minor to Person B. Might have been accidental. Might have been intentional. Person B reacts savagely. Police show up. Ambulance shows up. Janitors have to clean blood off the walls and floor.
I never saw anyone actually get killed, although that did happen in another school in my district.
I’m sure the water throwing didn’t occur in a vaccum. Aren’t too many folks that go looking for 3 on 1 odds.