Musk could simultaneously be a numpty at Twitter and a superb engineer at SpaceX.

You imply that skills are context-free black or white - that is a terrible way to think about people or the world IMHO. And you can’t ignore changes over time either.

Not the kind of engineering numpty he's shown himself to be. All engineering absolutely requires humility for situations outside the realm of your expertise.

But, the fact that he so clearly doesn't know when he is out of his depth in the first place is the real tell.

Like management, engineering is a discipline of means divorced from ends. There are certain vital skills that are shared amongst engineers regardless of their particular domain, and those are the skills most important for an engineering manager to have.

A computer engineer without those skills is merely an amateur physicist. A software engineer without those skills is merely a programmer. Ask a quant with no engineering background to put their ad-hoc scripts into production one day and let's see how that goes.

Musk might know some science, but that doesn't make him an engineer.