Just because they obviously lack knowledge doesn't mean they aren't smart. Perhaps they realise that they've neglected their intellect too much and are now attempting to fix that... I have no clue, there isn't really enough information in your post to judge. Of course, a lot of people try to seem intellectual when they aren't, and those people are annoying.
I say test them some more!
Bring up a new, thought provoking topic, which doesn't really require extensive knowldge to discuss, but which would probably spark a lot of interest from actual intellectual types. Maybe a nice controversial ethical issue or something. I think from people's reactions to things like that, you should be able to work out if they're smart people who've neglected intellectual matters for a while, or if they're idiots trying to seem smart to save their self esteem.