There is of course some genetic components in potential abilities.
But I strongly believe that most of the differences we are seeing are built on compounded interest of environmental factors, starting from a very young age.
Being "99.9 percent identical" doesn't necessarily preclude substantial genetic variation in intelligence just like it doesn't preclude such variation in height or skin tone.
I was asking what the basis is for your confidence that it positively isn't substantially genetic.
We know that intelligence is highly heritable, which leaves a few possible explanations, genetics being one of them (along with prenatal nutrition, prenatal lead exposure, etc).
If you're going to claim that genetics is only a small part of the reason that it's heritable, then that has its own burden of proof that needs to be met.