The theory goes as follows:
There are a number of traits associated with giftedness whose connection with intelligence seems tenuous, at best: creativity, great emotional depth and intensity, keener senses, unusual sense of humor, unusual and almost obsessive interests, etc. These are the traits that make gifted people seem weird. And all of these traits stem from a higher-than-average intelligence.In other words, gifted people come off as "weird" because they think differently and they think differently because they're smarter.
But why would having a higher IQ necessarily make one think differently? It might, if higher IQ reflects greater problem-solving ability, greater ability to see abstract relationships, or other cognitive skills that are qualitatively different. But high IQ might reflect a quantitative rather than qualitative difference. Maybe gifted people just have "higher processing power:" they think in the same way everyone else does, but they do it faster and more efficiently. Maybe their brains do the same things everyone else's brains do, only better. In which case, being gifted wouldn't make you act "weird." It would just make you better at a debatably wide range of intellectual tasks (depending on whether you subscribe to a general intelligence theory or a multiple intelligences view). It would not produce the divergent thinking and greater intensity and sensitivity many gifted people exhibit.
My experience with gifted people leads me to believe that high IQ reflects both a quantitative and a qualitative difference. Gifted people have more processing power, but they also process things differently. I don't know if one causes the other. Maybe they process things differently because they have more processing power or--more likely, in my view--they can process better because they process differently.
I don't think I agree with the orthodox theory, but at the very least, we need more evidence before we adopt it wholesale. I doubt we should completely dismantle the orthodox theory, but I do think it needs to be questioned and tested--expecially by advocates for the gifted.