I think what is more confounding is that such signs can be both mild ASD and brain immaturity/slow development. In particular, I am thinking about the child of a family friend who appeared to me clearly mild (beyond borderline) ASD and was classified with an IEP for ASD by the school district in K. Interestingly, this child also had a couple of savant traits (give him any date and he can give you the day of the week immdediately, etc.) that disappeared after the ASD signs improved substantially many years down the road. It struck me as odd that the savant ability disappeared as his behavior improved substantially into the "borderline" range - one of those mysteries of the brain.
I don't think this is mysterious. It is just two cases of developmentally normal growing up. The linked article already describes how various behaviors that look autistic are often really just various forms of immaturity that are grown out of.
In the case of disappearing savant skills (and there was a thread here a while back with several examples of this, e.g. our DSthen3 could rattle off the elements from memory but has long since forgotten them, and can't even remember doing it) my theory is the gifted toddler's mind is in high gear, but unsophisticated, so they may display savant-like skills. As they grow up and become relatively more sophisticated their brains have a lot more skills than "mere" memory/calculation feats, so basically their brains have better things to do, and so the savant-like skills seem to fall by the wayside (imho).
