As you know, big ad agencies, especially traditional ad agencies, are full of shit. They want desperately to seem relevant and current and will say whatever it takes to bring in the most relevant and current people, especially in digital and social media. Notice I said "say" and not "do."
They'll tell you about all the cool stuff they want to do but it's all talk. They'll bring out the shiny objects, mood videos, apps, and show you where the pet project incubator is in order to convince you how with it they are. And how valued and needed your contributions will be. They'll throw a bunch of cash at you to sweeten the deal. And you take it either because you want the money or you truly believe they mean it. Poor you.