I’m also Jewish and from Melbourne so I can completely understand where you are coming from and why your son’s nonchalance concerns you.
The one thought I had regarding their indifference is that because the Melbourne Jewish community is quite supportive of trump, due to his support of Israel, they perhaps didn’t see musks action as antisemitc because he is such an avid supporter of trump himself.
I could be wrong, and it doesn’t excuse how you feel, just a different perspective.