I've recently been nominated as a committee chair at work by my male manager; the funny thing is that he's on the same committee
Do this mean he likes me more than in a professional way, or wants to get to know me better?

It means he thinks you possibly have leadership abilities -- or at least he wants to find out if you do. Don't disappoint him.

(Do you have leadership abilities?)

Or maybe you're the best qualified person out there?

It either sounds like you're doubting your own abilities or you believe that he has feelings for you. Do you want him to have feelings for you?

Or perhaps he thinks you need experience and that by leading a group he is in, they can help teach you more skills on the job.