I am Aspie (note - "am", not "have").
My initial reaction on seeing the photo was it's nothing.
When I saw the first one, I also thought it's nothing.
I've made similar gestures to friends (tap my heart and then raise my hand up, arm stretched out, to show love and wave goodbye). I've also done the occasional maneurism that I've immediately said "whoops, that's looked a bit Nazi" afterwards.
Autism, by it's nature, means a lack of social awareness. But, somewhat paradoxically, it also means a heightened awareness of social behaviour - because autistics spend our whole lives monitoring social norms and masking (it's fudging exhausting).
So that's brings me to the end of the first gesture. Musk will know and understand the social context within which he is present.
If he was excited or tired (both very plausible), it is perfectly reasonable for him to make that gesture as "I show you love" and forget the optics. It was also off centre etc and not definitely a Nazi style salute.
We then reach the second one. That IS exactly a Nazi style salute. But could still be put down to neurodiversity (Nd is a contextualisation for some "behavioural issues"; that is distinct from being an excuse. They are, however, close lines).
At this point I was still in two minds. I've watched it numerous times and come to differing conclusions.
We then move onto the extra context:
I.
His reply on X. He didn't distance himself from it. He didn't recognise it as an error and say so.
It may take a few days for him to realise that - I know it does for me sometimes.
II.
His history of being supportive of the likes of Tommy Robinson, and if I remember wasn't he positive about apartheid?
The full picture makes me think it was a Nazi salute.