"Never be the smartest person in the room," is an advice meant to keep you on your toes. As with all popular advices, this one's also flawed.
The logic behind that advice is: if you're smarter than everyone, then there's no one to challenge you with new ideas. However, wouldn't your ability to think originally be the primary reason you're the smartest? Wouldn't using your talent, rather than just talking about it, be the value of those talents?
It seems that everyone's really arguing about the definition of smart.