Plus, I've noticed that with some people, their great knowledge and/or intelligence concerning a particular issue, combined with confidence (and maybe a dash of social 'deafness'), can come across as arrogance. Sometimes it took a while to figure out that they were open to correction, and hella smart.
I would've missed out on their insight had I applied a heuristic as simple as "arrogant people aren't smart".
Ignorance is not opposed to intelligence. Arrogance is a flaw that can reduce the benefits of being smart, but it doesn't make someone not-smart.
(Unless you're using 'smart' differently to the conventional meaning, which is an unhelpful thing to do.)