This looks more like a shadow than a silhouette. Also, nothing is in focus. Composition-wise, I'd eliminate the shadows surrounding your subject as they are distracting. I'd have the subject and the light area, but nothing else.
I don't find shadows to be the same as silhouttes. Maybe I'm wrong, or maybe it's up to each individual. But in my opion, whether it means much or not, I do not feel this meets the challenge.
My guess is that other commenters have probably mentioned the whole "I don't think a shadow is a silhouette" or something along those lines. Which, the way it was defined in the challenge description as "Silhouettes are created by backlit subjects, which causes them to appear solid and without much, if any detail." But, by the dictionary definition, your shadow of a figure smiling is technically a silhouette... anyway, with that out of the way...
It's a nice image. It certainly conveys a mood. I only wish the lines were really sharp.