Because the gifted spend so much time at their gift, they tend to develop habits by choice that are similar to habits of Autistics, who develop them out of reduced ability to do otherwise. That's my guess. Poor social skills can come from hardwired lack of ability (Autism), or from simply not socializing much (gifted). It's not quite that simple though. A lot of gifted people are very social. Actors, for example, are generally more social, but gifted.
Depends on what kind of gifted you mean too. Super high IQ gifted or just very talented at something?
The real difference is in whether the behavior is caused by a neurological problem, or a combination of high intelligence, talent, or whatever. The cause is the difference.
Then again, there is a reason the Mensa site has all kinds of links to other sites dealing with psychological and neurological disorders.
Sometimes it can be a chicken/egg discussion, but not always.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...