I also think that excitement =/= passion. For example, if you look at the top chess player - Magnus Carlsen - he always looks bored talking about chess, and yet that's what he does all the time and is the best at it.
Serious question: Does Magnus have a team of people that he works with? Do they enjoy working with him? Do they think he is boring? Is he the type of person you want to work along side?
Whenever I've observed him seeming bored I've assumed it comes from him being mentally so many steps in front of the interviewer. He's already evaluated all the positions, variations ad nauseum prior to being asked about them. Even if he did have something interesting to say it's unlikely he could put it into words that would resonate with the audience. I assume if he actually didn't have passion for chess he would've retired by now as his record is already good enough to be one of the all time greats.
Take the above with a grain of salt though, as it's probably just me projecting from my own experience as an IC that spends a lot of time working in a fairly specialist/abstract role.