The sitting still bit is the part I would attribute to temperament. I've known some ND (or even delayed) kids who would just sit and stare or do the same thing over & over for much longer than 15 minutes. I've also known gifted kids who can't sit still for anything.
I don't mean to keep shooting down what you are probably thinking of as signs of giftedness, but I think there's a good reason that IQ tests are rarely done on kids younger than 2 1/2, and generally aren't considered really reliable until 6 or beyond. I'm not saying that it's impossible to ID kids before that age, but for the most part we just have to wait and see.
