I'm sure you wouldn't have entered this in a candid challenge if it were not a candid, but except for the fact that he is not looking at the camera makes it seem posed. The lighting is excellent, and screams "studio," and his smile looks a bit canned, but probably the biggest thing is that there is not background of any kind to give the shot "context," so it is difficult to tell if it is a true candid or a posed portrait shot.
For one reason or another this doesn't feel candid... I'm not doubting you but it doesn't convey the candid feel to me. However, I won't mark you down for that... benefit of the doubt.