I guess it is the hairlight that separates him so clearly from the background, which is why I asked if the blurriness was created afterwards. But yes, photos against backgrounds like this one, where without the use of fill flash the boy's face would have come out way too dark, tend to get this very clear outlining ... which is enhanced by the fact that surrounding light reflects off his hair and seems to put a "pencil outline" around him.
Which is no critique at all. Just the attempt to find an explanation for the effect.
I like how you worked out DOF here!