You gather in the top part after finding the keycard, and then activate the console to begin the event. My guess is someone looted the card and didn't use it until there were only like three of you in there, so the event triggered without the group.
If you die, your loot is transported to that locked room with the crates.
If you win, the locked door is open, and all of the loot from the people who have died before you is now yours.
After a while, it ends up being a very impressive hoard.
The boxes also spawn some pretty high-tier stuff.