From Scrutable,FWIW, I've just seen unsubstantiated claims that the prank in question involved accusing the target of being a wanted sex offender and pretending to put them under a "citizen's arrest". Allegedly, the prankster has other videos on his channel where he performs this "prank" on people.
I still don't think it justifies shooting the prankster, but if true it might represent an angle for an attempted legal defense.
https://www.youtube.com/watch?v=gUccLZPRGjk
I've watched the first 20 seconds and it looks like a big bloke and his sidekick are trying to pock a fight with a stranger who is a lot smaller.