It's highly unlikely that he's SUPPOSED to be secretly smart, at least as most of us would perceive as 'smart.' The moviemakers wouldn't have gone into unnecessary depth with a minor character.
However, he does seem:
1. alert and observant, e.g. when Shenzi and Banzai are too distracted to notice the cubs sneaking away.
2. ingenuously honest, e.g. when Shenzi and Banzai claimed they didn't know who Simba was but Ed nodded anyway.
3. perceptive and understanding of deeper issues. He knew perfectly well that Scar had betrayed them, and he knew what he wanted to do to him.
Ed may laugh insanely at seemingly everything, but could it simply be because he's an optimistic, cheery soul who loves to have a good laugh? Or could it even be that he lets himself sink into a giggly, humorous state to hide from something, perhaps troubling thoughts or a traumatizing memory? These kind of questions are the reason fanfiction exists. In the context of the movie as we
officially know it, Ed is a minor character who is probably mentally ill and nothing more. BUT. Who says we can't give Ed an unprecedented background story?
As long as it doesn't contradict the movies, I'm all for speculation about this!
(I myself have had a fanfic idea about this floating around in my head for quite a while now.)
