It's probably just Zod's failed attempted coup...although it could also be a flashback to Brainiac's assault on Earth and Zod's attempt at repelling it. I was kind of hoping too that they would include this from New Krypton as a way to show him the hero he once was before his fall from grace(it's shown in the "Superman Unbound" DTV) , but since technically that was "Donner Zod" probably won't be the case. I do still think we will see Brainiac in the sequel, but I'd be surprised if he was mentioned or shown in this film.
About a month ago there were some spoilers by some guy who had allegedly been to a WB advanced screening. I don't have a link now but from what I remember