I mean, at the risk of making this political, I think we can find at least one ostensible billionaire that most people are not arguing for the intelligence of. I'll let you figure out who I might be implying.
I think intelligence is helpful, but not a necessary component to become really rich. I think there can be combinations of luck, opportunity, and charisma. It doesn't hurt that silicon valley investors appear to be the most gullible people on the planet.
I don't know the guy, but I did hear reports of him constantly drinking and smoking weed at the office, and him claiming that they're making a "human based operating system", a claim that does not make sense.