I've known 2 people with NPD and... Might want to go into detail what 'intelligent' here means. Both are as dumb as rocks and can't stand a chance against me in a debate, but one (A) is VERY street smart, and the other (B) VERY people smart. The street smart one was the more subdued, pathetic snivelly guilt trippy kind 'HELP ME I'M PURE I'M A VICTIM I'VE BEEN WRONGED', and the people smart one was the very charming pathological liar.
People I know, who also know B, describe him as 'very intelligent', 'articulate'. B is very skilled at appearing faux smart, unless the person they are talking to start poking holes and digging deeper- which, most don't. He knew which words to say, he knows which people he could hook in without them asking many questions, and if the veneer starts cracking, he knows how to gloss (with BS) in such a way that it looks like he still knows what he's saying. The craziest mind boggling part was that once those mutual friends met me they said I sounded like HIM. I found out that he was copying ME- how I think and how I word things, but since he doesn't have the real deal, poking at him has him fall apart FAST. That was a strange, strange thing that happened.
In a drunken (?) (he sounded drunk) stupor, he admitted he WAS copying me, because he realized how much attention and ego-stroking that got him. I was in a mix of fascination and utter befuddlement; he was both smart enough and dumb enough to do such a thing. He also can appear confident and authoritative, which I am guessing was also something he artificially did or even, copied from someone else, he even could act quite convincingly like certain... Celebrity figures, god knows how or why. But really, once you crack him he either goes pathetic-snivelly like A, or 'HOW DARE YOU UNMASK ME' and would actually go physically violent. These people are in actuality extremely fragile.
EDIT: Oya. And about person A, the reason they come across as 'smart' (superficially) is because they know who to snivel to, and how.
I make it sound pathetic, but their methodology sadly works. It at the very least is very successful, so if you want to use that as some parameter of intelligence, there you go. But I'm thinking the reason these folks (ASPD included) widely appear as 'smart' is because if someone can outmaneuver you easily, they can easily appear 'smart', even if intellectually speaking, they might not be. People widely call A & B smart but their brains are made of mush. One sobs their way out of anything, the other charms their way out of anything, but same idea.