I'm calling this one out. I'm not going to ask how you managed to defeat 4 of them, but if you watch the video, there are two issues with you "winning" this encounter.
1. The Infernal Council requires you to defeat ALL 8 Sith Lords. You only beat 4. Not finished.
I'm not sure what you did, but you definitely didn't beat the Infernal Council.
You need to pay more attention. Each of the 2 players beat 4 Council Members. That's a total of 8. They beat them all.