That's silly. Sometimes it seems like people really, deep down, want other people to be closet racists.
It certainly looks like a Nazi salute. But there are reasons to think that it's unlikely, too. He's supported Jewish people and causes in the past. Which isn't really in line with being a Nazi.
And he is seriously awkward and weird and socially unaware at the best of times. Not just a little bit, a lot.
IMO it's kind of a wash, I could see this meaning any number of different things, or nothing, coming from him.
The other question is, if it is meant to be a Nazi salute, would the Trump administration, or Trump himself, support that? I don't think so - I think they are committed to support of Israel, and I don't think Trump is bothered by Jewish people or Judaism personally. They have some support from the Jewish community right now which they seem keen to keep.
If Musk were to decide to go in that direction it's very likely to be a wedge between him and the government. Though I think that is likely to happen in any case eventually, Musk is too much a globalist to fit in well with some of the things the Trump government is likely to pursue.