So why did they show a shilouette of Dedenne instead of Pikachu if that was the reference
Well, since Dedenne is a pikaclone it has a slightly similar silhouette, so I think the idea is that a casual observer may just think that yeah, that's a Pikachu, while Pokemon fans can recognize that something's off there. Plus there's the whole history of silhouette based gags with Pokemon that I think is being alluded to in a more vague way.
Now, it's Dedenne
specifically because that is Kuroha's favorite Pokemon (
here's him taking it for a walk at the Shueisha office).