Pomegranate is a punchline that the guys overheard in a hotel room. They didn’t hear any part of the conversation except “pomegranate!” and it’s become an inside joke since it was used in the music video for Celebrity Status! :)
There are also a lot of things about the band that are important, I can’t really name five specific ones since it’s mostly opinion-based; just know they’re really sarcastic. You can learn a lot about them through their YouTube videos and tweets!