Gifted Children Find Heavy Metal Comforting
shows some sales figures from 2006. Of the youth-dominated genres we get something along the lines of:
The part in bold is the problem with what you said. From the original parent post, this isn't talking about youth-dominated genres of the entire music market, rather it's talking about one specific institute. The population there happens to be 120,000. Given that 6% are into metal, so the obvious answer there is only 7200 out of 120,000 are into metal. That really is quite a few given the number of people the the specific population of the institute in question.
So really, Swift Kick is right. A few people are into metal. That doesn't prove that the vast majority of gifted students (at least ones belonging to this institution anyways) are into metal at all.
That all being said, comparing nation wide ratings to a very specific survey is apples to oranges. Of course nation wide data wouldn't apply to a specific set of date.
And on top of that, Swift Kick is probably right, they probably do annoy family and friends and act like total douche bags and listen to metal to cope with their own insecurities. I know I did when I was a teen, and I was a total fucking douche bag.