If Elon Musk did this because he wanted to (not make a statement, just to achieve some other goal he has) then that‘s not really art. If he did it to make a statement about how different rules apply to billionaires and he wanted to point that out then that to me would be an interesting artistic expression, sure (though he probably wouldn’t do that).

For well more than a century artists like Duchamp (e.g. Fountain from 1917) have been playing around with what turns something into art and makes it valued and where then line between art/not art is and what that has to do with explicit and implicit rules.

To me graffiti in its contemporary form in general but also specifically Banksy is a pretty natural continuation from that discourse that fits right in. That to me has always been the additional layer to any work by Banksy, whatever other (often obvious) statement the artwork might make.