Hello,
It seems this log was edited : (or a bug i dont know)
https://www.warcraftlogs.com/reports/Tm4cN7nfkxJhXwyt#fight=2&type=damage-done&source=11
Has been reviewed by the warlock discord, conclustion : manually inflated damage of at least chaos bolt / incinerate by around 50%
This guy even steamed that kill here : Twitch
Where we can see his real dps : 5k8
Thank you