I don't know if I can be considered one of the intelligent one's on this form, but I am only 18, and yet have much to learn.
I believe that our form gives the impression of intelligence because Diplomacy is a game that takes intelligence to play well, and if you don't play well, you probably won't have fun, and not having fun, you won't stick around, and won't become one of the core members that make up the forum. Also intellectuals attract intellectuals, and so because we have a base of intellectuals, we interest more intellectuals in staying on the forum.
I have always had a love for useless facts that basically equate to party tricks, because I have such a store of them that whenever a topic is breached, I can usually give a related fact that is in some way interesting. This seemingly endless supply of information gives people the impression that I am smart. Just the other week, my sister (who is in college) texted me that her professor asked her class if anyone knew why barns were painted red, and she was the only one who knew the answer, and the only reason she knew that was because that was one of the random facts I knew (by the way, barns are red because Iron is the pigment used to make red paint which was the most abundant pigment at the time and so the cheapest paint). But not only knowing those facts, but to be able to bridge them with assumptions and to be able to come out with the most logical conclusion of how something works when you don't know is also something that is used to boost people's view on your intelligence, it makes it seem like you know everything.
The downside of this is that people can often misinturprit your eagerness to inform, as cockieness and you being condesending, and that can be a turn off.
Anyways we all are nerds and geeks who play board games with their free time, so we're all probably somewhat smart...