We got a new junior developer about a year ago. He acted exactly as you described. I don't consider myself as a superstar dev but I do know a thing or two. So the guy questioned every thing I did for months. At first I welcomed the challenge because it forced me to look up things I haven't been 100% sure about. But when months went by the questions got more and more irrelevant to the work he was doing. He was asking questions for the sake of questioning me not for the answers.