Ok, I have pulled out my Ellen Winner book, which has quite a bit of information on artistic giftedness. Her finding is that the Draw-A-Person test correlates only weakly with intellectual giftedness. She has a fascinating case study of a boy who at age 5 was rated as drawing as well as a 14 year old. He did not have a similar aptitude for reading or math.

So, Isa is right. Like many other traits, this one is a possible sign of giftedness, but not an outright indicator.