How did they exploit fame?

I once saw a pic of flo and some other people standing on a corner while shooting the boss, but wouldn't that kill him along with the forgotten souls? Can someone tell me how it worked, I don't think it's useful anymore anyway

Forgotten Souls used to drop 195 exp, so people would set their aimbot so it would only kill them instead of the boss, exponentially spawning more as they died.
Kabam fixed it with the latest patch, they now give 0 exp.