Yes we can speculate a lot, but the sad end when it concern handicapped children in the past, were most likely that they were put out in a forest. There where little empathy for mental or malformed people in the societies, especially if they were born that way and this was something that didn't end in our western world until our more recent modern days in the 1800's. It's still a tradition in some parts of the world even today to get rid of them and some folks in certain places have never seen a disabled person with their own eyes, because they are hidden away or just killed. As an example, In the former Soviet union, no one ever saw any handicapped children outside, they were all locked down in institutions. ( If you do believe that people were better before, rethink).
The very thought that a quite rough society with an extreme adoration for manhood, should have kept a disfigured child does not sound very credible, not even when the writers try to overcompensate his shortcomings by telling us how intelligent, beautiful and strong he was.
Purely logical, I would say that he most likely just were very agile and lissome in his joints to such degree that he seemed to be boneless.