The Return of Megg

I gone through Cairo Station a few times and the achievement still isn’t popping for me. I’m following this guide The Return of Megg achievement in Halo MCC

Am I missing something?

Edit: Nvm I guess what I had to do is not kill everyone and just hide somewhere in the room out of the elevator to finally get it.

I also didn’t see the dedicated thread for ahievements. Sorry mods.