Innate ability is obviously a huge factor, but they don't learn to speak (or their colours) in a vacuum. My kids have all learned to speak at different ages, they all have different personalities, strengths, weaknesses, etc. But it's not 100% nature, environment counts...
Just like some parents provide a rich environment for developing speech, others are good with colours, or ball skills, or music, or maths. And when we have a child with the innate ability to pick something up easily when the inspiration is in their environment we may be inclined to feel the child "taught themselves". Gifted children can learn a skill way in advance of their peers without any more exposure than an average child of their age, I absolutely believe this happens. But I suspect that often gifted children have gifted parents who naturally do things a bit differently to average, and because the inspiration/support is part of their lives in a way that feels completely natural/normal to us it is perhaps somewhat invisible to us that we are providing better than average support to learn a skill.
Some families wouldn't ever go to the park without a ball. They probably don't think they are hot housing ball skills. It has never once in 9 years occurred to me that I should take one, at least not before I got there and saw someone else's. But I wouldn't leave the house without pencils and a jigsaw in my bag.
