That’s not what happened at the panel.
DC showed the Blur Studios’ CG trailer for Arkham Knight, which earned a lot of cheers and applause. It was pretty loud, so you can’t blame someone for not hearing what came next, but it wasn’t an Arkham Knight delay.
While people were applauding and cheering, they specifically said that Batman: Arkham Knight would be released later this year. After that statement is what most people didn’t hear, and they said to prepare for the return of Injustice. The “not a 2014 title” statement applied to the new Injustice, not the Batman sequel. No other details about the new Injustice, such as who is developing it, was revealed but it is apparently on the way…just not this year.