Questions about example sentences with, and the definition and usage of "Unability"

A: The sentence is actually sort of grammatically incorrect which might be why you’re confused 😅
I think it’s meant to say:
His inability to stand still, aka (also known as) being in his own world.

The idea is that he is restless and can’t sit still. “Being in his own world” is a phrase that means he’s daydreaming or oblivious to the things around him.

Hope this helps!