It’s possible you are interviewing that one charismatic fraud, but what’s more likely is that you’re just interviewing the mediocre developer caught in a lie.

Or a introverted developer who's nervous and not very confident at interviews. Which is very likely.

I have yet to meet the first introverted developer that does not open up and become enthusiastic when asked to talk about one of his (personal) projects. I’ll admit they may exist though.