I assume it's a shadow, but it's eerily in the same shape and colors as BG, like literal foreshadowing by nature. enlarging it makes it too blurry to see anything. I don't think it would make the person too tall when you compare it to the poles in front of the bridge entrance. How high are they? they are about the same length as what would be legs in the shadow image. In my view, the shadow person is coming down a bank on the side of the trail, so he wouldn't really be that tall - he would just be on the edge of an incline making him higher than the trail.
the real height and thinness of BG is discernible in that picture, IMO (very tall and thin). I can even see his stride - left hand down by his left leg, which is crossing in front of the right one, right hand in pocket or on hip. even looks like a hood on his head.
if it isn't BG, what is it a shadow of? Maybe GH can figure that out.