It also takes a fairly smart person to be genuinely funny, I think. The easiest types of humor to emulate are crude humor, sarcastic humor, and physical humor/comedy. But to be genuinely funny in a way that isn't overtly insulting to anyone takes some smarts, so maybe that's part of it too.
I have three daughters, the youngest of which I perceive thus far to be the smartest (they are all really smart) but what was interesting was that she was doing physical comedy far before she could speak or walk.
Basically making initiating funny body movements seeking us to mirror her and to do coy little hide and seek games.
Not only is it terribly cute, seeing her think up funny games like this to play and watching how she giggles and laughs is really interesting to see how it expresses her personality when she can't even formulate words yet.
That's probably closer to the truth. My 9 year old nephew was more mature than his sibling and cousin because his interaction was almost entirely with adults, but his 2 year old brother is WAY ahead verbally at the same age because he interacts with his older brother ALL the time.
