Robert's new home healthcare aide has been asking more questions about his medical condition, which is a good sign, I think. It means that she's trying to parse his differences, and I think that action of parsing is a first step toward understanding. You need to set Robert against things you know and things you don't know and let your brain run through the logical actions of similarity and difference.
As a graduate student at Columbia, I used to teach a composition course that tried to incorporate the basics of logic, and similarity and difference was one topic. The essay topics were guided, kind of used as a Platonic dialogue teaching tool. The similarity and difference module was designed to show students not just that similarity and difference were relative (Aristotelian), but that the two concepts shaded or blurred into one another, that articulating similarity in isolation or difference in isolation is nearly impossible. You cannot talk about one without the other.
Robert is only different through ways in which he is the same.
His love of the swings is a love of movement. It is one of the few times I see him happy in an unadulterated way. He is a happy child, but his happiness is always tempered by a great patience with the people and the world around him. He has to wait, he knows involuntary stasis, and yet he has to will a sort of stasis in order to get by in this world. His only way to really express his final frustration is to burst into tears and start howling, which he will finally do, as would we all, if we found it impossible time after time to say what we meant or even try to say it.
On the swings he can move without effort, any effort at all. He is in glorious, extended motion, and it must feel good to move without having to think about it, move without labor. What he can experience through swinging is exactly what any of us would: exactly the same sensation. But the joy he takes in that freedom of movement is beyond anything any of us can appreciate, not truly knowing stasis.