You can arrive at a completely different conclusion, but how is intelligence a factor in the choosing?
The reason I believe there could be a link (maybe a very small correlation; nothing big) is my own "anecdotal" observations. I've seen how a lack of intelligence can keep people from becoming a vegetarian. Often people don't address the issues in a well-reasoned, objective manner but react based on their emotions/desires ("but I just couldn't give up cheese!") or more often, simply avoiding the topic altogether.
I have not once, ever, come across a sound, cogent reason for eating meat (barring edge cases--just talking about the typical case). But I've come across many different sound arguments for avoiding eating meat. The overwhelming truth and well-thought out arguments of vegetarians impresses me.
For more context, I wasn't always vegetarian. I was raised with meat at every meal and I would complain if I didn't have meat. It was ultimately the cogency of the argument for vegetarianism that converted me. I would convert back if I came across an argument for eating meat.
So after years of hearing poor arguments from the meat-eating side and sound arguments from the vegetarian side, it makes it believable when someone suggests there might be a link between vegetarianism and intelligence.
(I'm actually quite impressed that this Hacker News discussion hasn't degenerated. In my experience online discussions about vegetarianism often degenerate into childish snark. Thanks for keeping it real.)