If you took the time to read my post, and watch the video you posted, or even had entered the encounter yourself on either hard or nightmare, you would have realized that something was wrong.
I gave very specific values for the health of SOA and Mindtraps in Nightmare. SOA has slightly over a million, the traps have 218k HP.
They killed the boss on hardmode not nightmare. The boss was not correctly toggled to nightmare. Our guild also killed the boss while it was in that state, its not much of a feat.
Yup, in the video the Boss has 890k HP, Mindtraps have 25k. This is on Hardmode, despite the title. It was probably before Nightmare got fixed given that it was posted the day of the fix, so the instance was set on nightmare, but it wasn't a nightmare encounter. Certainly not a world first.