If anything, if one feigns surprise, they are acting in bad faith. I agree with the title of the article -- don't feign surprise, e.g. if somebody gives you a gift you knew was coming and pretend you're baffled by its appearance -- but do show surprise when someone you know who is intelligent is missing a small puzzle piece in their knowledge space.
Not in a belligerent way, of course, as the author points out: use it as an opportunity to educate. I ain't about to berate a friend of mine for not knowing something, but it would be quite disingenuous to hide my surprise; in my eyes, that's comparable to talking down to them.