I think your right with the clip statement. From the way its bent its looks like it GOT bent rather than supposed to be bent. If you were to straighten it out that tongue part would then clip behind the little loop.. it that all makes sense lol.
ALSO! If you look at the way the tonguy piece and clip end are bent you can see they are a little bent in the same spot. My theory would be a small peice of rope or something was clipped in there and it got pulled on, or too much weight put on it, and it would then bend that tongue part down and pull it out of the clasp... And its really looks like that is how that bend in it would have occured.
I must be the only one who's gonna say that this a vintage musical instrument , what ? A 19 th century Jew Harp ! Of course it suffers from being bent but I bet if you straighten it out flat you could pluck out a rhythm . Looks like it was met for a child and looks homemade . IMHO , Woodstock