Musk is definitely by all accounts a genius, at least in certain domains. See my other comment about non-transferrability of expertise. I think the reason there are so many genius morons is that people assume their expertise magically transfers, and so they skip doing the work required to gain expertise in a completely different area.

"I can code, so I can reevaluate history and political science." "I can do organic chem really well, so I can read a creationist polemic and dismiss all of geology because it seems to make sense to me."